Ok so DD is in pre primary and I *think* I've got it down to a fine art lol.
Sunday Arvo I make 2 homemade treats (cake, muffins, biscuits, pikelets, slice) that gets us through the week.
About Once a month I make a lot of sausage rolls and a zucchini slice which I freeze in portion sizes.
For morning tea she has a Tupperware sandwich keeper with fruit bread/saos/vita wheats, fruit and 1 homemade treat. That goes in an insulated bag from Tupperware.
For lunch she has a mountain bread wrap/roll/sandwich with tuna/chicken and salad, piece/tub of fruit, sausage roll/zucchini slice and 1 homemade treat. That goes in an insulated rectangle bag (smash brand I think) with a small ice brick.
The hardest thing for me was finding containers she could actually open independently and thinking if things she could eat without making a mess over herself. She's also now wanting stuff she can eat quickly so she can go off and play.
Hope that helps