Pile pillows between them so that if they drop something in that direction, it stays at hand level and they can retrieve it themselves.
I got a small, soft photo album and put photos in of people and occasions in our lives. Dd would spend ages over this turning pages at her own pace thinking about things. That lasted for a few years, actually.
keep activities with you by your feet. Then as one thing gets discarded, pass them another. Some familiar and some new. When you stop for a break, just shovel them all back into the bag ready to go through it all again.
DD’s tummy could never do spinning things in playgrounds then back into the car. Sometimes she could not even do too many roundabouts.
Books might not be safe for tummies but an activity like Barbies needing clothes changing or Duplo might work fine.
Yes yes to bowls, cloths, water bottles, change of clothes, wipes, plastic bags.