The same night that I made my near-disaster salmon bento, I also did the sandwich cutter experiment and packed the resulting sandwich into a snack bento for the next day. Normally I don't eat such a large afternoon snack, but I had an appointment after work and knew that supper would be a bit delayed.
This was the (slightly blurry) sandwich that I ended up with after my test run with my sandwich cutter. After making the tuna sandwich, I still had a good deal of bread left from the two pieces I had used.
I wanted something a little sweet, so I made a second smaller sandwich from the ends of the bread with some no-sugar added apple butter. Apple butter is sweet enough on its own; it doesn't need more.
Both sandwiches went in the box, along with a blue silicone cup. I had a good deal of carrot left over from making the salmon bento, so I cut that up and added it to the two empty corners of the box.
The next morning, I added the fish-shaped hard boiled egg that had been setting in the fridge over night to the box, and was ready to rock and roll!