Going back to school without going back to the traditional schoolroom is the concept behind Communiversity, an offshoot of the Free University that's offering some interesting, inexpensive classes taught by local people who feel they can teach you a thing or two. Among the 40 or so courses, which usually take place at the teachers' homes, are yoga, backpacking, winemaking, photography and techniques in getting information about everything from your your home computer to your car. Clases for the mentally handicapped cover gardening, money management, cooking and job-hunting techniques. For a brochure, call 937-5669 or write Box 451, Beltsville, Md. 20705 . . . If you've got valuables at home and want to make a quick record of them for insurance or appraisal purposes, for a fee you can have it done by Photographic Inventories (363-8661). Photographer Judy Peacock will photograph the entire contents of your home, or just a corner. The minimum fee is $55, which includes 24 color prints. Each dozen extra prints cost $22. fYou get all the negatives . . . Musically inclined travelers will appreciate the assistance of the new International Guide to Music Festivals ($6.95, Quick Fox, sold at bookstores), a roundup of major jazz, classical, folk and bluegrass festivals in North America, Europe, Asia and Latin America. It offers a windfall of information about each festival, including an address for inquiries, descriptions of the location and past performers, and information on accommodations and tickets.