In addition to the other great suggestions here I also like these things:
This Travel Pill case it is large enough to hold 4 large pills per section, and has 4 sections per day.
The Flip and Tumble Grocery bag . This bag holds a surprising amount, and because it fits on the shoulder, not carried in the hands, it makes it easier to carry.
Table Mate tray table this is the cheaper version of what others suggested, and is a bit less sturdy, but if you are on a limited budget, it works great.
OXO Good Grips Products I love the can opener, but any of their Good Grips products work great. They are specificly designed for people with arthritis.
I feel the most important one of all, though, is a fuzzy comfort blanket . People underestimate how much better you can feel just from wrapping yourself in something soft and warm for a bit. Even if you still hurt, it can make you feel like you can cope with it better.
EDIT: I just thought of another thing. The whole homemade coupon book is cheesy, but the truth is that offering to help them with housework, do some laundry, or even just spend time with them is an awesome gift in most cases.