There's a Target immediately north of the fence of the E-W runway area, aka the North 40. If you're weight limited, bring only those items that can't be replaced or are specific to you, then buy what you need at Target, such as towels, folding chairs, small cooler, etc. When done, donate the usable items at the Goodwill in the same strip mall as Target. There's also a grocery store in that same strip mall.
What everyone forgets - medication. If you take any precription meds, get your Doc to write you a script and stash in your wallet. If you need a refill for whatever reason, there's Target. There's also a Walgreens a bit further north on the highway.
Also bring a backpack. You'll want water, munchies, raingear, etc during the day on the grounds.