My son has a degree in physics and is soon to start his PhD on solar energy. He has also taken to Pokémon Go, which is essentially a collector's game which gets you out and about. I slightly get it, having been (full disclosure) a collector of train numbers when I was 12. It does have a strongly social aspect - we were amused when he gravitated towards and starting chatting to a couple of young French players while wandering around La Rochelle. You can tell Pokémon collectors by the way they walk around with the mobile phone in a particular position and gather in clusters.
I've been wondering whether the collector's instinct can be called upon a bit more in language lessons. Schools are already aware of the powerful effect collecting can have - think of those keen youngsters collecting merit stamps and stickers from teachers. Some collect detentions, of course.
In a language lesson here is a simple idea which goes some small way to satisfying those who enjoy collecting. It's a simple variation on the task type where you tick off words you hear during a listening comprehension exercise. Instead of that, why not, every now and then, provide students with a list of TL words they might hear during the lesson. This could be a simple and quick add-on to your normal lesson plan.
Let's say you know that your lesson is about healthy living. You give each student a list on a strip of paper of about twenty words or phrases broadly on that topic (body, food, exercise, football, vegetarian, smoking etc - you can also include general words) and they have to tick off any they hear you say. You tell students they can only tick off words on their list which they hear you saying, not words they read. You could make the activity competitive, praising or rewarding the students who find the most words.
How do you know for sure if you used the words? Well, you wouldn't want to make this too accurate or time-consuming, so you could use your memory or make an educated guess which words you uttered. The checking-off of the words would be an excellent and natural plenary activity. There may even be disagreement about which words were used - another excuse for recycling the language.
If you did this activity several times over a term you could even keep a league table of who did the best if you or the class were that way inclined. Students could keep their lists and stick them in books.