Yes. Honestly it depends on the flight and class and destination. If I'm going into LOS then I need to bring snacks because there's no 7/11 (or anything else) that I can hit if I get hungry. If I'm flying C/F I generally don't bother as they have the same snacks on the plane as I find in the lounge. I have been known to take a beer or coke (1) from the lounge to drink while waiting to board a flight.

Like anything else these items will disappear from the lounge (as is already the case at UA) if people abuse the privilege. But a can now and then or a couple of bags of crisps doesn't fall into that category.