It depends on the group. There was a casual yoga thing in my hometown where after they would all go for a coffee. Some people arent into that and do just want to do it and go home, but others like getting out and socialising after. Unfortunately theres no hard and fast rules. Women are just people, people vary a whole lot in likes, dislikes, and what topics they like to talk about. Ive seen heaps of comments from people of all kinds all over the internet and making friends in general gets much harder after university. And harder again once kids, jobs and relationships get in the mix.
But you could just try a casual hello, before yoga/pilates. If they are receptive give chatting a go and once class starts go do your own thing. Little hellos and casual small talk can build familiarity where you can see if they might be up for being friends.
Sims can find seeds laying on the ground. So if insects, gems, and small animals are still spawning then gardenings still doable. If they have access to water then so is fishing. With a fire they can roast things. Thats food sorted. Socialising is doable if they befriend a wild horse. Not sure how theyd get clean, so theyd be stinky and cranky about that. But theres a few options for sims to entertain themselves without items. Come winter theyd die without shelter.