I think the rule of thumb is to drink about 1 bottle (600ml) an hour in fair weather... in HOT weather, I'd up this quite a bit, maybe 1 1/2? So one bottle per 20 miles sounds like very little to me, especially if it was really hot.

A bite or two every 45 minutes is also not very much, even if you actually do it... Eating every 20 minutes might be more in tune with your energy needs, on rides longer than an hour...