Stealing someone's order

What do you do when someone steals an order? I was very polite about it just earlier but I wonder what you guys are actually able to do? I was standing next to this guy, while what looked suspiciously looked my order was being bagged up, and taken almost immediately by the guy standing next to me, I did wait about 7 minutes just in case, but yeah, pretty sure it WAS mine, no number called, because who else orders a free Double Quarter Pounder with cheese and a £5 meal deal like a fat ass? Anyone?

Do you try and keep a profile? A good look out? And shouldn't there be a better effort to check tickets of people?