Hmm... I'll think of something..
At my school they have Padlet Sandoboxes that we use often in Geometry. IDK if there was an offline version available, but it might be something to look into.
There might be an offline Version of blooket too, as we use them in EarthSci.
If I have one today, might test that out.
-Update, Tried blooket without internet, No-go, sadly.
Also have another suggestion that would also be very helpful. In our classes, we use something called "Gimkit". Sort of a mix of Blooket and Roblox so to speak with different game modes. We use these often, and are usually very helpful.
Mostly the things we use require an Internet connection, however. Maybe look into-long term a laptop with a SIM card slot or something along the lines. That way you can be constantly connected wherever you head to. Dell would be a good starting point- but I can't tell if the drivers for it are all fine with the SIM, so if you need be, just make sure it would have correct drivers available to use it.