I live alone in a lovely walkable part of this city with many restaurants where all my friends who live on the outskirts of town want to meet me all the time. I agree with many of the posters that eating out is one of the harder things to get in control. Here's some of the strategies I've used to cut down:
1) I always prepare lunch for work, either the night before or on the weekend. There's nowhere awesome to get food near there, and it's easier to get through the afternoon after a homemade meal anyway- less calories. It also takes less time to simply eat than to go somewhere, order and wait. I spend the extra time walking around or just having quiet time. Sometimes I work a little bit and that allows me to escape earlier.
2) I bring snacks to work, too- one for mid-morning, one for the afternoon. If I don't do this, I'm more tempted to go grab some enormous sandwich or something because I'm starving at meal time. If I pack everything, I never feel ravenous and enjoy my own food a lot.
3) If a friend wants to meet for lunch or dinner and I know it's going to get pricey, or if I'm not particularly compelled to go out and would rather blow my wad on another meal down the line, I tell them I'm busy but suggest we meet for coffee and a walk, or just a walk and I bring snacks or a fun beverage. It's novel. People love it.
4) I invite people over for simple homemade cocktails and small snacks in the afternoon.
5) I second the notion of inviting people over to cook together and making that the experience rather than going out and spending a bunch of money. The added bonus is that my house does not close, so I can spend more quality time with friends in an environment where I get to control noise level, number of people, etc. Plus my nice guests usually bring fun fancy things.
6) I avoid group dinners out like the plague. I've said I have to work late and shown up for dessert and a drink. A dinner with eight people gets out of control. Long before I was into Mustachianism, I resented that particular expenditure. So I skip it.
7) I've started buying bulk stuff at good deals that I can't finish on my own (for instance, 12 avocados for $3 at Grocery Outlet yesterday- impossible to crush myself, despite the deliciousness of avos). Then I suggest a trade for something else. A good friend of mine has chickens so we're doing an avo/egg trade this week. This gets other people into cooking and preparing their own food, so I am in good company.
I am not a purist by any means, and I think that helps me not feel deprived. I almost NEVER buy clothes, gadgets, or new anything, so I am a little more generous with my food budget than other things. I am ok with that and am enjoying the process of cutting back bit by bit. If I wind up going out spontaneously and it's fun, I don't fixate on it. It happened, and hopefully it was worth it. Hope it helps.