For short walks, the basic equipment is comfortable walking shoes and comfortable clothing.
Most bicycles will be fine on the trail which is for the most part surfaced with fine crushed limestone. Experienced riders tend to prefer a hybrid (cross between road and mountain bikes) as thin tires can sink into the trail surface and make the going slow. People with mountain bikes tend to prefer hybrid tires or conservative mountain bike tires with just a little tread in the center and lugs on the edges to handle mud. Barring the extreme tire widths, any bike will work just fine. Be sure the bicycle, particularly the saddle, is comfortable. If you do your own maintenance, check the bike over before leaving for long trips. If you don't do your own, take the bike to your friendly local bike shop for a safety check and tune-up.
The Great Allegheny Passage runs along side an active railroad in many sections, it's recommended that you bring earplugs to help you enjoy a good nights sleep.
There are chemical toilets at the campgrounds and GAP access areas, but limited potable water available. We recommend that you carry at least a quart of water more than you think you need. Take advantage of towns along the way for water resupply.