Actually, I think Merlot's idea of "services provided"would be easy for one person to do. 91 "coupons" for the Birthday girl, each worth an hour or more of your time through out the year.
+1
Rides to the hairdresser/grocery store/doctor/dentist
help with housecleaning
ironing
weeding the flower bed
washing the windows
putting things away for the winter (picnic table, lawn furniture)
Not to be disrespectful, but at 91, she probably doesn't need more stuff. And those who will have to deal with her stuff, probably don't need her to have more stuff. My parents have tons of notecards, address labels, etc. They don't need more stuff--most of us don't need more stuff. But they do need help with routine household maintenance and that is what my brother and I do when we make the 2400 mile journey several times a year. We de-clutter (in five years, we've made but a small dent) and help with routine maintenance stuff.
Since my brother and I live so far away, we have often discussed the "how are we going to deal with all their stuff" aspect. We are both adults, have our own stuff, and live across an international border. There are very few things either of us want to bring home--maybe if we were in our 30s, but not now. It is most annoying that people give my mother trinkets--little statues, magnets, etc. These are things she doesn't need and only add to the clutter. If I find s/thing I bought her (one of those foot eggs to get callouses off, for example) still in a drawer, I get rid of it. She isn't using it, therefore, she doesn't need/want it. We have asked that they not do that--that they go and visit with a meal-on-wheels or to help weed the flower beds or take the dock in and out instead. It is easier, I guess, to pick up a trinket than to spend time helping with things that help keep them in their home. And, if the birthday girl lives in a facility, she has limited space for things. Money is good, but if she lives in a facility, she may not be allowed to have more than a certain amount of money every month if on the State's dime.
I understand the hostess wants to make it fun, but some consideration re: what the person is going to do with all that stuff (maybe only 3-4 people will be invited, but if 40-50 people show up with 91 things in a goody bag....) would be nice. I'd probably talk to the hostess about that, but I'm ueber sensitve to people giving the elderly worthless trinkets.
Have you seen the movie, "Up"? 
