You could do a scavenger hunt. Great in the park, give them a list of things to gind and set them off. If they complete a little present as a reward. Can be made more challenging. Have also done this with guides/brownies where we used disposable cameras or mobile phones with cameras. List of photos they had to take. Not people which may be a little weird. But colours, a particular word, animal, vegetable, mineral etc.
Papier mache is also cheap and great for miserable days stuck in home. Make something small or large, use scrunched paper/kitchen roll tubes as a base and build from there, you could have it as an ongoing rainy day activity.
Fabric pens on old t-shirts
Is you mn local up to date with days out or whats going on??
Pick your own, do you have one nearby.
Go to a woodland and collect lots of dry leaves for a collage, this may be for 1/2 term as leaves will be coming down by then.
A small pot of quick growing lettuce cut and come again.