For cranky hands, I like this key turner, a gas cap opener like this, and this weak-hand-friendly box cutter (feels so much nicer than ripping stuff open or using scissors, but also check out electric scissors or rotary cutters if you do things that frequently require scissors). Not exactly assistive, but these feel amaaazing to hold and roll around in your hands when they're stiff. You can put them in hot water for a few or micro them briefly at 50% before holding them and it's magical.