Well, I did all the standards. The photocell didn't work great in the circuit but I could get some effect by completely wrapping a finger joint around it for darkness. When replaced with the FSR it worked quite nicely.

Processing, however, was a problem. After failing to figure out the issue in the lab, I had no more luck the night before the lab was due. I followed the helpful instructions from Nate but without success. I could run the paint program by pressing different keys on the keyboard, but not with my cirbuit. Will work more on this.

As for the mechanical component - I got two! The first is a kong - a dog chew toy. This is one variation of it -
it's meant to be be squeezable and tough. Inserting the fsr in the end
slit does the job ok. However, the ball has rubber ribs which come
apart and together when the ball is squeezed. They are too wide for the
fsr as it, but could squeeze it with some padding.

kong kong-and-fsr

The second is a mason style glass jar. It has a rubber seal which works quite nicely with the fsr - basically an "open, closed, somewhere in between" sensor for the lid.

jar jar-and-fsr