Breadsticks?
rice/corn cakes? there are plain ones/marmite ones/snack a jacks come in all flavours but have loads of msg/
I use a mixed seed bar for dd1 (gluten and dairy free, and ASD so food issues too!) - have a look for "9 bar" in ocado, they stock them I think. you can get them plain or carob topped (dd1 thinks its choc!)
do you have a Holland and Barrett near you? they have quite a good range of fruit bars (like humzingers) and also have a coconut bar which dd1 loves.
all quite sugary, unfortunately...
how about pancakes/drop scones? they keep quite well, and you could work up to grating apple in (I know you're not wanting to spend loads of time initially, but maybe later on).
fruit/veg fritters are also great.
dd1 has eaten courgette cake, and beetroot cake, both disguised as chocoalte cake, and they went down a storm.