Tell her that your knee is bothering you and that she will have to do a good part of the towing of stuff She can get a little cart like they use for groceries. And it is unreasonable to expect that you should have known what she wanted. Limit your amount of time you spend at these things. Maybe go with her for one hour, take the purchases back to the car, and then take a nap, or have lunch somewhere closeby, or read a book.   mg