Learn to pile stuff...I am not a fan of putting foam around hand tools, unless one is an A&P Tech. The foam just takes up too much space.
Personally I don't use Systainer's for hand tools nor most other non Festool stuff as I have found the cheaper and larger Ridgid tool boxes and Packout's to hold tools far more efficiently. The number one thing is organization. Everything has a place and the tools always get put back into their place.
But hey, if you want ideas on filling that tool box I can recommend all kinds of must have tools to buy LOL Snap-on stuff is expensive.