The carry-in policy is buried in here, but here it is as well.
"Fans may not bring into Miller Park any cans, glass containers or alcohol. Soda, water or juice must be contained in factory-sealed plastic bottles. Guests may bring food items into Miller Park using appropriate containers. All bags, purses, fanny packs or soft-sided coolers must be 16" x 16" x 8" or smaller and are subject to inspection. Hard-sided coolers are not allowed in the ballpark. Only food purchased within Miller Park will be allowed into Suite areas."
The most important thing here: You can bring your own food and drinks into the game. If prices at Miller Park are too high for you, stop at a gas station before the game and pick up some cold bottles of water or a hydrating sports drink to bring with you.
I just want to make sure everyone is aware of the Miller Park carry-in policy. With the hot days of summer here and the Brewers playing three-straight day games in 90+ degree weather that could feel like it's over 100, remember what you can and can't bring in.