I also don't see the big deal with a child having a memory that isn't happy, happy, 100% perfect experience. That is what is wrong with this generation of kids, this generation of parents try too hard to only have perfect memories for their kids. It is good to have a less than perfect memory and you know what chances are this trip and this experience will stay with your boys longer than if they had got that silly box of popcorn. It also taught a valuable lesson that will stick with them all their lives(much more than you just saying it) That if you want something bad enough you have to prioritize it and do it first.
Ruin your trip hardly, give them a memory that they will remember possibly all their life, definitely. I still remember the vacation at the lake that it rained everyday and the most excitement was watching to see if the stream would flood our cottage. I can still describe that cottage and what my Mom did and various other small things about that week, and while we went every year almost all the other weeks of fun have slipped from my mind this one is still strong after 40 yrs.
Ruin your trip hardly, give them a memory that they will remember possibly all their life, definitely. I still remember the vacation at the lake that it rained everyday and the most excitement was watching to see if the stream would flood our cottage. I can still describe that cottage and what my Mom did and various other small things about that week, and while we went every year almost all the other weeks of fun have slipped from my mind this one is still strong after 40 yrs.
on some of our money
. People might just wait for the free popcorn and not buy it. 
Our daily lives are usually go-go-go though.
This is why it is never worth it to pour your feelings out on these threads. Better to just stick with asking questions, providing answers and sticking with the facts. Otherwise you have people like this responding to your concerns.