Fall is the time to buy a meditative cushion that you can take with you when you meditate outside. You can buy a clip and attach it to your belt loop. You can also use the cushion when you meditate in the house.
Go to a large box store or a sporting goods store such as Dicks and ask for a Sportsman's Cushion. They usually are colored camo and are priced $5 to $10. I have a link to Amazon below as well.
I would be a flexible one that retains your body heat and is plasticized so it is not affected by rain.
Here are a few examples:
There are many other types: