Little & often. Keep hydrated & fed to keep blood sugar levels up. I find on a long ride, that I keep sipping at isotonic drinks and as regards food, I'm one of those sad souls that likes isotonic gels - specifically the High Five energy gel plus ones in raspberry flavour! Other things I've been known to take include flapjacks, malt loaf, banana, fruit cake, oatcakes, energy bars (I like the SiS cherry & vanilla ones). The other thing is to be prepared and take with you more than you think you'll need. Plus if you get the opportunity to stop off for a cuppa - do so. Take as many opprtunities to eat & drink as you can.