Originally Posted by IceTrojan
I noticed most of the replyers (is that even a word?) are from the US, and OP is from the UK. Perhaps it's a little-known UK rule? Just playing a little Devil's Advocate here....
No, there are no such rules, either in the UK or the USA.
The OP was pulling our leg - and flying RyanAir - which flat-out prohibits bringing your own food and drinks, because it wants to sell all food and drinks. Just like a movie theater or theme park. It's all about revenue and has nothing to do with aviation rules.