I can't say we do this every day - but when we can:
nice fresh bakery loaf and butter (DD2 likes tea/ DD1 has juice)
Muffins/ buttered or with Jam (tea/ juice)
Bagels (w/ tea or juice)
soft boiled eggs & toast soldiers
scrambled eggs/ hard boiled eggs (both very fast - but you can do the hard boiled eggs earlier)
raw vegetables nibbles: (get an economy pack of peppers, brighter colours the better), cucumbers/ carrots/ celery/ cherry tom - girls like them plain but less finicky kids may like them with houmus or ranch dressing or some other dip.
fruit - I really like to treat them to seasonal fruits. So we should be entering prime apple and pear season soon, grapes improve from now too, around December satsumas/ clementines get good/ Feb-April is slow, but by May you can get a nice range of berries (we wait until British produce is available). (check out 2 for 1 offers and think about using extra as break snacks/ after school snacks).
Make your own sandwich - so have all the meats/ fillings/ spreads + extras (mayo/ mustard/ lettuce/ tomatoes/ etc...) but let them work out their favourite combinations.
Pizza/ Quiche - homemade or store bought. You can buy ready made bases and decorate as you like - which can be a lot of fun too.
Philadelphia cream cheese and bread sticks. (we make little hedge hogs first - use table spoon & scoop out a large lump, then decorate with bread sticks as spines & use bits of olives as eyes/ nose).
definite treat for first nice warm day of spring: ice cream cones/ Popsicles
definite treat for cold winter days: mug of hot chocolate (with marshmallows)
autumn treat: hot apple drink: heat up ordinary apple juice, but add a cinnamon stick & a few cloves. Just warm it to steaming hot, don't let it boil.
Puff pastry treats: We use an old Delia Smith recipe (from her Christmas book) and sprinkle grated mature cheddar & use parma ham in centre, fold the dough over it - add a bit more, fold the dough over again - bake & in 15-20 minutes - gorgeous hot snack. You can just do plain cheese ones, or add things like olives or anchovies (although our DDs won't touch them).
HTH