You want as much exposure and communicative need as possible that matches your level. Making friends, doing activities, concerts, whatever. Expect to regress when you get back, but imagine you are building as dense a language network in your head that future you can draw upon when needed. It mostly won't me something you can draw up on a moments notice, but can kinda prime again by re-engaging with the language slowly over a few weeks at a future date. I personally would shoot for deep more than wide exposure. So if you are into something like French cooking, spend as much time around that than spreading yourself broad. This is mostly bro-science, but this would make the memories a lot more robust against forgetting. Don't let this rule ruin your trip though, if you want to see a million things, those memories are a lot more important than language bits.