WHO SAYS you can't build a better mouse trap, make a bed without tucking in the sheets or even bake pineapple upside down cake in an egg pan? Listed below are a few gadgets and home improvement gimmicks that have a good chance of surviving next year's garage sale:

With the rising price of gold you may be tempted to invest in a do-it-yourself gold leaf kit from Absolute Coatings, Inc. The kit contains real gold leaf (not paint), sealer, brush and step-by-step directions. It is recommended for leafing picture frames, wooden boxes, whatever needs the Midas touch. The Kemp Gold Leafing Gilding Kit is available at craft and paint supply stores for $9.25.

If you can get the gold off your hands and keep your refinishing spirit, the C.H. Tripp company has Color Rich Wood Stain available in 15 natural wood colors. The stain, the manufacturer says, is easy to use; wipe or brush it onto previously stained, varnished or bare wood surfaces and let it dry. Base primer and claear finish are also available to make a wood grain effect and protect surfaces from water marks and scratches. Available at paint and hardware stores.

Nefertiti eat your heart out. Mongtomery Ward is offering a complete collection of stainless steel flatware designed to commemorate the treasures of King Tut. The 52 pieces, complete serving for eight, are available throgh cata99.

For those who haven't already ODed on R2D2 and C3PO, new easy-to-hang vinyl wallcovering from Sherwin-Williams illustrating scenes from "Star Wars" is available for $9.99 a roll or $2.49 per strip. The wallpaper can be used for murals or to cover wastebaskets, closet doors and school books. If you wish to remove it, you tug firmly on a corner and pull it off the wall. Available at Sherwin-Williams paint stores.

New lighweight polyurethane foam furniture for children is claimed to be indestructible, (But then the manufacterer doen'st know you children.) Each piece - sofa ($35), chaise ($30), foot stool ($12) and chair ($25) - is covered in 100 percent factasy jungle land print cotton. The kids will like the fact that it is soft and cuddly and that it is too smally for the grown-ups. Available at Hecht's.

Owens-Corning Fibreglas Corporation has developed a new bathub and shower surface that is said to be more resistant to scratches and slipping. A mild abraisve such as baking soda or detergent is supposed to be all that is needed to clean the fiberglas surface. Available and Noland Co., Falls Church, Rockville and Silver Springs; Thomas Somerville Co., 6th & Buchanan Streets NE and the Waldorf Supply, Inc., Fairfax.

Removing mildew from bathroom tiles is the aim on life of X-14, instant mildew stain remover, which claims to erase mildew with the wipe of a sponge. Care should be taken not to get X-14 on your clothes because it is a bleaching agent. Available at suppermarkets and hardwarestores.

An Eggory is, suprise, a Telfoncoated surface which aims to cook omelets, hamburgers, sandwiches French toast and even pineapple upside-down-cake. The two-section pan is hinged so one omelet half can be flipped over on top of another half which contains the fillin. Available at Hecht's for about $25.

Metal Ware's new "Kar-Mate," an eight-piece coffee set dinclude a four cup coffee maker, two cups and spoons, a detachable 12-volt adapter, safety bracket to hold coffee maker in place and a console that fits over a car's transmission hump. The Kar Mate plugs into ins your car cigratte lighter and is available at WooDies for $29.95.

Hammacher Schlemmer has, it thinks, invented the proverbial better mouse trap. The Sonic 2000 transmitter emits high frequency sound waves that are supposed to drive rats, mice and squirrels acase. The transmitter is not supposed to affect people or pets. It plugs into a standard wall outlet to keep a 2,000-square-foot area rodent free. Available through the Hammacher Schlemmer catalogue, 147 East 57th St., New York, N.Y. 10022, for $129.95.

Fiberglas roof shingles that claim to be fire resistant, rotproof and longer lasting than conventional asphalt shingles are available from Johns-Manville in a variety of styles. Each shingle has on the sun's heat to seal each shingle on the roof into a single unit for protection against sun, wind and rain. Available at Hechinger's home improvements stores.

Samsonite has developed a durable, all-weather, super-tough, mesupholstered furniture with canvas-like "body glove" fabric to be stitched like conventional needlepoint canvas or left plain. A color brochure is available by writing the Samsonite Corporation, 11200 East 45th Ave., Denver, Colo. 80239. Special kits are also available for designing outdoor furniture.

Instant Vinyl is new to repair cracked furniture and luggage. It is available at True value Hardware Stores, Bloomingdale's and Montgomery Ward's for $2 a tube.

A new concept in convenience bedding - an all-in-one "Sleepmate" - combines top sheet, bottom sheet and pillow case itno a single unit. The "Sleepmate" is made of no-iron cotton and polyster and comes in several patterns and colors. Available by writing Providence House, Suite 18, 1539 Monrovia Ave., Newport Beach, Calif. 92663. The twin set in $19.95 and the double $22.95.

Since Medieval days, the unicorn has been an eusive beast. Kaleidoscope (P. O. Box 13655, Altanta, Ga. 30324) has captured the fabled creature in many forms enchantingly stuff stain and corduroy unicorn ($30); as a delicately small charm dangling from a tiny 14K gold chain ($150); adapted from a 16th century wall hanging and hand-painted on Italian tile ($40); featured in a colorful amber and green stained-glass panel ($85); reproduced from a 14-century tapestry "La Dame a la Licorne" on a 10 inch limited-edition Limoges plat ($45) or hand-etched upon a old-fashioned glass ($16.50 for a set of 6).

Levitz furniture store has hired the internationally famous designer John Weitz to create the first of their designer-named home furnishings. The designs reflect Weitz's concept of simplicity in elegance. His gently curved modular units are upholstered in neutral fabrics, treated with Scotchgard.

Not only does the Cuisinart food processor blend, puree, slice and shred, but it now chops its price. The Lexan plastic base model has been reduced from $160 to $140 and the heavier metal base model from $225 to $200. According to a Cuisinart spokesman it isn't the competition that has forced the new price, it is a new model - the DLC-7. The new model will be smaller, have a stronger motor that makes less noise, a 30-year warranty, and a Two-button on-off switch. The DLC-7, which will be available sometime in the fall, will retail for about $250.

Hamilton Beach has come up with a new Model 2002 Electronic Food Processor and 16 digital speeds on its control panel that converts from the English system for "mistake proof" processing (errors are conveniently blinked to the user's attention). However keep in mind that the more intricate the processor becomes, the more there is to break down or go wrong. The Hamilton Beach Food Processor will be available in November for about $145.