I buy the smash lunch box(carrier) and use nude food containers for everything. The smash range of containers for sandwhiches and snacks is easy for the kids to open themselves and so far hasn't leaked.
Then you can add an ice disc if you need to on the hotter days.

Our school is nude food only outside, had to search for easy to open containers. I found the tupperware containers were difficult for my boys to open without help.