Where are you staying? Plan a day for the geyser basin (West Thumb, Old Faithful, etc), a day for the canyon area, a day for the Mammoth area, a day to do nothing but relax and walk around, and a day or two for other stuff that you find. You will find ranger led seminars at several places; they are usually pretty good. Make sure you spend an hour or so in the Old Faithful Inn; wonderful old building. The Yellowstone Hotel on the lake is also worth visiting. There is also interesting stuff around Cody. We love Grand Teton so spend a little time there.
Food: Nothing special that I can remember. It is almost all typical national park, expensive, cafeteria style food; nothing special, but you are not going there for the food. We have eaten at the Old Faithful Inn restaurant; it was good.
Above all, be ready for the crowds. Double the amount of time you think you will need to travel and see things. Many times traffic will be bumper to bumper 20 mph or less; sometimes behind a bison road block; just sit back and relax. Despite the summer crowds, Yellowstone is a must see and well worth it. We have been there many times; my next trip will be in the winter.