Not got an Esso filling station with a shop anywhere near you? I went to 1 earlier [got back about 10 to 12]. Apparently they're open 24/7, though they lock the doors & only serve through 1 of them security hatch things after 2am [the guy might have said 3, I forget].
The only thing is, they tend to shut at about 10pm or 10:30 for about 1/2 an hour [shift change & cashing out the register, or whatever].
Might be worth checking out for future night-time snack requirements.