I always carry a banana for rides longer than 40 miles, just in case. I have bonked a couple of times on the way home, late on a Sunday, with no shops open and it's not fun.
If I haven't eaten it on the ride I have it as a treat for the last few miles. On full day out rides I'll probably carry a ham or cheese and salad sandwich, usually with some sort of pickle on there. The gents I occasionally ride with have a little chuckle to themselves while they eat their flapjack/malt loaf/energy bar but I can't stand the cloying sweetness when I'm out and much prefer 'proper' food.