I think that he's telling you to pick fun activities that are closer to home AND that don't stress YOU out (you're going to be put out and whiny yourself if it's not the funnest day ever because you dropped a lot of cash for it--and believe me, I have MORE than been there).
You seem to imply that this kind of behavior happens at other times than a high stimulation, high stress (good stress though it might seem) environment. If this just seems part of his personality, then you're going to have to get control of your own impulses and anger and angst first, so that you can help me learn some social rules about when and where and how to complain.
My most difficult to discipline child also happens to have for lack of a better term a natural "eeyore" personality. If she'd decided that going to the zoo that day was going to be an irritation to her, then even renting a stroller, having a cooler full of her favorite foods, and the promise of a big purchase at the gift shop wouldn't hold in the whining, the fussing, the dawdling, the snark, the pouts, ect.
What I learned to do that helped BOTH of us not totally lose control and damage our relationship was to cheerfully and *non-punitively* say, "You know, I thought today was a good day to come to the zoo--but you know what, I'm not having fun either. Oh well. Let's get out of here and go get some ice cream/hang out at the park/go home and make a picnic instead. It's okay to not feel like going out sometimes, I don't either." The first couple of times I had to do something like that, it escalated the behavior until we got into the car, because to be honest it had been a huge all day power struggle outing at that point. I learned how to deal with my anger/angst at losing out on $$.
As much as it sucked for everyone, until DD had gotten better at expressing her needs without being hurtful, we didn't go on big trips or places that *I* couldn't handle turning around and walking out of if that's what was needed. Now she's honest if she feels like she's having an off day, I try to accomodate that if I can, but she also has learned and internalized better how to deal with it even if it doesn't go her way. That's after lots of work at home and school. Some kids just have a harder time learning how to do that than others, it can be a really fine line to walk sometimes because you don't want to ever crush the "different drummer", but OTOH not teaching a child (appropriately and gently! You can't blame the kid if you stuff it until you explode because you can't deal with it anymore) how to handle the out-of-sorts/grumpiness doesn't do them any favors as they get older, I'm sure we all know some really unhappy adults who don't know how to avoid peeing on other people's cornflakes. I think with a young kid, it's NOT about being a brat, it's hard for even adults to learn how to deal.