I'm sorry about your grandmother's stroke.
You already have been given so many good ideas.
How about some herbal tea bags? Peppermint helps digestion, might be needed with hospital food
A variety might be nice.
A nice long newsy letter to read.
slipper socks... fast to make and warm
Some new photos of you and yours for her to show the nurses.
Raw nut mix could be for her or your grandfather.
Does your grandfather do crosswords? May be something to occupy his time there if he does when he's waiting for her to get out of pt or such.
Maybe a good read aloud book that your grandfather could read to her.
Change for parking, vending machines, etc.