I eat tins of sardines or mackerel fillets a lot when I'm peckish - I keep a stash in my drawer at work and usually because I have to work late and get hungry I'll have one of those, it's quite heavy on calories (200kcal or so), but that's about the same as a chocolate bar or packet of crisps and it's almost zero carbs, and cheap too, at around 30-40p a can. I tried snacking on nuts, but could eat a pound bag of walnuts in one sitting if I had one.
I also have those fruit and nut shots sometimes, they're about 100kcal and about 15g of carb, and cost about 50p. Apples are quite good too, depending on the size, around 12-16g of carb and about 65kcal.
It certainly is true for me that eating carb-heavy food makes you hungry sooner - I used to eat porridge or cereal for breakfast, and couldn't get to lunchtime without feeling hungry, but now I'm eating a low-carb diet I have full-fat yoghurt and nuts and seeds instead, I can make it easily and have been known to forget until around 2pm.