Do you have children or a partner or is it just you?
With kids / other half
Outside games - setting specific time to kick a ball / play tag / hide and seek / treasure hunt with toys they already have can be fun and a way to be sure you get time together
Picnic outside- head to the garden or a walk if you have no garden, take the food you would have eaten anyway, blanket on the grass and lots of chatter while you eat.
Morning coffee in the garden or nearby communal green space
Board games
Reading either alone or together
Craft days using whatever odd bits and bobs and recycling you have
Gardening/ allotment
Make sure you have a library card, they do some fun free activities as well as books magazine and audiobooks. Some even have puzzles and things available
Apply for an allotment, they cost pittance and are good fun plus you get plenty of food out of the hard work
Sign up to Freecycle and any similar Facebook pages in your area, you have to be quick but plants, games, toys, craft kits, and all sorts to be found on there which can be lovely treats to pick up and really boost your mood
Take up fishing if you can, it's not free but licensing can be cheap for some adults, as little as £5 If you are disabled, children are free, and some places don't require you to purchase an additional permit. You can get fishing equipment on the free cycle pages and things like sweet corn or earthworms from the garden can be used as bait rather than buying maggots and pellets from a specialist shop.
Become a citizen scientist and do nature surveys and so on. Great fun and gets you learning about the natural world
Most of the ideas involve being outdoors because it really is a mood booster