Can I bring a small soft cooler to a theme park?

Yes, but check the specific park’s website first. Most theme parks allow small, soft-sided coolers (roughly 14x14x14 inches), but hard coolers and larger ones are almost always banned. National parks and city parks don’t care—bring whatever you want. The real risk is forgetting the “soft-sided” rule at a corporate park, so check their bag policy before you go.