If you're worried about getting a drinks bottle, a 750ml buxton water bottle fits a normal bottle cage pretty well.
I prefer the 1l Volvic bottles as a) more water, natch and b) the square shape means that the bottle deforms and "squeezes" into the cage and I found it holds it there alot better. When the Buxton bottles near empty it rattles arounds and keeps falling out. Or maybe that just has something to do with my technique...
Kate - you need a drink for definite. Out of food and drink, drink is more important.
Last summer I ran out of drink on a long route and only rode 3 miles without drink in the heat until I reached a village shop, needless to say I nearly passed out from dehydration.
Get a bottle cage! lol.
This. 100 times this. The thought of going out without fluid would horrify me to the point of not going!
Contrary to what I said above, now that Im stretching out the length of the rides, I shoe-horn a 1.5l bottle of Buxton into the cage normally; stays there well and generally by the 25-30 mile mark, I'll pop into whatever corner shop I can find, buy a 500-750ml bottle (depending on what I've consumed) to top it up which then does me for the rest of the journey/warm down at home. Although I'll also generally down a bottle of the Lucozade Sport stuff at my stop-off aswell. I have no idea if thats healthy, I just generally listen for my body to say thats enough. And then as for food, something light but whatever takes my fancy. Normally a choc-bar for a kick up the backside. Im no nutriotional expert, Im sure what I do consume on a stop-off would dumbfound some more experienced heads! Anyway, I ramble and digress readily were food is involved.
Get a cage!
NB, I am the furthest thing from a serious rider, and my avg speed is below yours, but everyone's gotta refuel.