For food we normally go to town if we don't get food from the vendors on the festival grounds. For breakfast we normally go to the Barking Dog Cafe. For Lunch/Dinner we go to the pizza place called Pizza Bar 66 or the St. Vrain Market for sandwich from the deli.
Although, the food vendors are hard to beat. They have gyros, Abo's pizza, ice cream, fish tacos, crepes, and I believe, a breakfast burrito place.
In between sets you can go get merch signed or meet the musicians at the merchandize tent and go shopping at the vendors tents. Or if you're artistic bring watercolors. The kids bring paracord and make bracelets. Bring low-back chairs and watershoes(I learned that the hard way)! Also, bring tubes to go tubing on the river (the river might be really fast this year, though). But trust me, you'll almost always have something to do
Getting a shower can be tough. At Meadow Park the water seems to always be cold lol, but the best place to get a shower is on-site. Always warm, clean. Privacy is not the best, but I just wear a swimsuit.
PS: don't forget you rain gear!
Good Luck!!