I don't do many long rides - am more of a local bimbler. But if going out for more than an hour or so, especially in summer, I'll chuck a piece of fruit and a packet of crisps in my pannier. There's always a roll of sweets in the bar bag anyway if I need a bit of oomph. For away days, it's basically a standard packed lunch (sandwich, fruit, a pastry and crisps) but with some extra snacks like marmite rice cakes and salted nuts. I find I prefer salty to sweet - too much sweet food makes me feel awful.
When fencing competitively, it was loading up on pasta the night before, then eating little and often in between bouts. And keeping up the hydration. You really do sweat buckets when wearing t-shirt, plastron, jacket, lame and the rest of the shebang.
You can get rice pudding in individual foil-topped pots - Muller do them.