Avoiding the food rip-off at convention centers (and other places they overcharge you when you're trapped!)

Apologies for the light posting lately. Between trying to write a novel in a month, and traveling to a conference for work, I've had trouble finding the time to write.

The conference reminded me once again about the power of near-monopoly. In this case, there were maybe 5-7 restaurants in a convention center that must serve 40,000 or more people at once. As a result, not only were the lines extremely long, but the food was ridiculously overpriced. We're talking $5 for a slice of pizza, $11.50 for a small veggie wrap, and $4 for a 12-ounce bottle of juice.

Now, when you're stuck in a place like this for work, you may just get reimbursed for whatever you pay and so the price doesn't matter to you. (In fact, that's probably part of why they get away with it.) But a) I get a per diem, so saving money is in my own interest, and b) it bugs me to overpay in general, especially when the food is so mediocre. So I tried to find ways around paying the exorbitant prices:

• Buying food the night/morning before. Stopping in a grocery store is always a good bet. Even overpriced convenience stores are often a better deal than the convention center prices.
• Saving leftovers from dinner. This is easy for me since I have a smallish appetite and often have leftovers anyway. But if you don't, you can try to order big and/or fill up on appetizers or bread.
  
• Looking outside the convention center. Many convention centers will have restaurants (or grocery stores or convenience stores) somewhere within reasonable distance, but they may be hard to find. Ask various members of the convention center staff for help and directions; sometimes the official Information people won't tell you because they're not supposed to, but guards, coat check staff, and others are typically much more helpful.
  
• Bringing snacks and a water bottle. Even if you have to buy your main meal at the convention center, filling up a water bottle can save you from overpaying on drinks, and having snacks on hand mean that you can order a relatively small meal. And if you've got a long day, snacks can be crucial in tiding you over so you can wait to buy dinner until you're out of there.

Do you have any other tips to avoid being trapped into paying high prices for food? I think some of the same principles apply whether it's a convention center, an airport, a stadium, or anywhere else they overcharge you because you have no/limited choice...