You should always into account the reason the rules are in place. Some establishments have very nice furnishings (good carpets, expensive tabletops, etc.) that would be ruined if drinks or whatnot got spilled on them. If this is the case, then you should definitely be following the rules. Of course most of these places would probably also have some type of 'you ruin it you pay for it' policy as well anyway.
On the other hand, sometimes the rules are in place only for the establishment to make a profit (overly expensive food/drinks without allowing outside food/drink to make more money). In cases like this I myself would probably break the rules simply because I see that as bad management. If you have to resort to forcing people to buy your own refreshments to make more money, you probably shouldn't be running the business. If this is truly the case (money problems), then the answer isn't to require them to buy your own things. You just need to let people know that, to be able to continue to host tournaments, gatherings, etc. then it would be a great help if they bought things from you instead of going somewhere else. It also helps if you keep the price range reasonable (no more than a dollar for a slice of pizza or canned drink, things like that). TO's/hosts don't get to be jerks just because they're in charge, they should practice good manners as well, and maybe even more so than the attendees. Remember, common courtesy goes a long way. ESPECIALLY with customers.
To wrap up my rant (which seems to be what it's become), don't be a nasty nancy if you get called out on a rule. You should've been informed of the rules and regulations of the establishment some time before or right as you entered the building (if you haven't, calmly address the issue with the organizer and don't just yell and throw things. That doesn't solve problems.). The fact is, no matter what the rules are, they're there for a reason. When you break them, and you consciously know that you're doing so, you can't be mad that you're getting in trouble for it like you knew you would if you got caught anyway. Face it, it's your fault you got caught, take responsibility for your actions.