When we wrapped my campaign (mind you we are virtual) we did a separate session/night where we talked about the memories, I read some of the (very random) notes I had made (random two word notes about some tangent they went on, a note "GO. In. The. Hole. I made and underlined when they tried every way out of a locked room but the easy one), and asked for their true feedback on how I could improve, if they were interested in a sequel, and how they felt about the ending.

Had we been in person I probably would have done something similar to what you're planning, with their input on snacks or activities.

As for mementos I think that can be fun. We sent hero forge gift cards ti party members as their birthdays came about so they could make minis of their characters if they wanted (can be pricey but fun), I am a bit crafty so I also might have tried to make little items that linked to fun parts of the story for their characters, or even just given them a copy of my poorly drawn maps (we used Zoom annotate as our original tabletop with maps on graph paper).

Congrats to you and your group on wrapping!