I just gave my old ATB (pre mountain bike days) 10 speed to my dad

but I didn't like riding it because of wrist and back pain, BUT I did not have room for it along with my LWB (man is it big

) and all the other (ahem) "stuff" we seem to have to keep. So maybe something like saddle bags that fit over my back rack (not on) would work if removable Or a trailer that folds flat. Any suggestions?
Thanks