Step one – provide food. Consider the cost of 1 developer hour. If you have 10 developers leaving for lunch every day for an hour, and they have an average salary of 80-100k, that means that in order to pay them to stay instead of leave it would theoretically (ignore the fact that there is no overtime for a minute) cost you 400-500 bucks. So if you spend $50 on pizza, and get a single hour of peripheral work done during that lunch hour, you come out even. If you promote some scheduled lunch and learn or class type activities, you might make your workforce more valuable for a lot less outlay than sending them to a conference.
Step two – provide tasty beverages. This is the same logic as above – spend $50 on drinks that can be consumed at 5:00 + and if those 10 techies manage to wrap up just one more thing, (while enjoying a cold one) that amounts to a single hour of productivity, then you broke even. Anything more and you basically got free output from some of your most expensive resources. Even consider the casual conversations that can occur and free up more time during regular business hours.. it all adds up and I think it will be in your favor, and we will not mind at all.