Friendship $$$$$$$$

I've just started having out with my friends more and it's really fun but I don't have any money. We're all around 17-18.. I'm the only one without a job because I'm finding it hard to find one. We were supposed to have a picnic the other day and they all started buying coffee and food from the shops. They never want to do anything that doesn't involve buying things. I totally understand but I find it hard when I can't join in. What are some things we could do that don't really involve money. All I can think of is walking... Pretty boring