> how can I side-load my own programs into the Android edition?
If you are simply wanting to run your own BASIC programs in the Android edition of BBCSDL, that's most straightforwardly achieved by connecting your mobile device to a host PC using a USB lead, and mounting the Android file system as a remote drive. The directory which appears as @usr$ in BBC BASIC corresponds to the path Android/data/com.rtrussell.bbcbasic/files/ as seen from the host.
You can even run BBC BASIC for SDL 2.0 on the host and directly edit your BASIC program(s) directly within the remote drive, then you simply have to run them from the Android edition; this is easier than using the limited editing capabilities of the 'touch IDE'. It is probable that if your program crashes out you will need to force-close and re-launch BBC BASIC on the device.
If you want to go the whole-hog and create an APK from your program so that you can side-load it without needing to use BBCSDL at all, use the BBC2APK utility. This is Windows-only so that may be an issue for you if you're using a different OS (it uses the Apktool utility for the heavy-lifting so may in principle be portable to other platforms but it's not something I have attempted).