I think she wants to be friends

[SirPrizeMe]

Let's see, the words for politely declining to get beach towels, etc.

"Oh, you need towels? You must be really busy getting ready for the trip, with everything going on. Geez, I'm sorry but I have some plans for tonight and tomorrow so I won't be able to help you. (Sorry!) I wish I could. [here you could even elaborate on your plans - I'm changing the oil in the car, I'm watching a movie with friends, I'm going to check out a new museum exhibit, etc. Doesn't matter what the plans are, the point is to show that your plans take precedence over her needs, now that you are no longer married. ] I hope you're able to get some rest!"

As cheerfully as you can.

would that work?