We always finish with 20 minutes of meditation – sitting cross-legged on the grass. A typical setup is a zabuton (square pad) and a zafu (round meditation cushion). You are free to bring a blanket and a pillow. Note that most pillows are not firm enough to boost you up to support comfortable sitting, so you may want to consider a couple books to place under it.
If you can’t sit cross-legged comfortably, you may want to consider bringing a folding chair or a seiza bench.
You can Google ‘zafu and zabuton’ or ‘seiza bench’ to find suppliers, as many yoga suppliers offer these.
Here’s the Amazon link for the zafu/zabuton and one for the seiza bench.
Here’s an Etsy link.