how does one keep the bread of a sandwich from getting all soggy from the stuff inside (like creamy potato salad)?

Package it separately and make the sandwich right before you eat it, duh.

Tupperware/butter dishes ftw.

And avoid pre-making sandwiches with tomato on them, it's notorious for ruining bread, and will turn to crap.

put solid/dry stuff (salad, cheeze etc.) inbetween the bread and the soggy stuff

My technique is to lightly toast the bread, then let it cool for ~5 minutes. After, I make the sandwich.

At lunchtime, the bread has sogged all the ingredients' excess humidity, and gained its original mushiness.

This works perfectly, except for tomatoes, which just contain too much water.