AMTRAK's `ALL ABOARD, AMERICA' DISCOUNT FARES will continue to be offered on a limited number of seats for the rest of the summer. A $299 round-trip coach fare from New York to San Francisco allows for three stops, to be completed within 45 days. Early reservations are recommended. Refunds are available if cancellation is made prior to half an hour before departure. Phone your travel agent, or Amtrak at 800-USA-RAIL, for details. `CAMPING AMERICA'S PUBLIC LANDS', A NEW GUIDE from Rand McNally, lists over 4,000 campgrounds in America's national forests and state parks, and on government-managed land. It's published in two editions, Eastern and Western, at $5.95 each. Each includes maps, a list of fees, and details of facilities in the campgrounds. SOME CONNECTICUT FARMS WILL OPEN THEIR GATES to visitors for the 12th Annual Farm Tour July 11-12, sponsored by the Connecticut Farm Bureau Association Inc. Included are farms that raise dairy cattle, horses, apples, blueberries, Christmas trees, and more. For details, phone (203) 249-6208. AIR CANADA IS TESTING OUT NO-SMOKING FLIGHTS linking New York/Newark-Toronto and New York-Montreal during a three-month trial program. A survey indicated that 83 percent of the passengers on those shorter flights were nonsmokers and that an even larger percentage preferred that smoking be prohibited. Air Canada already has no-smoking flights on some of its Canadian routes.