For me:
Being outside in nature helps. Even more so if I'm able to take in the wonder of things that I'm guilty of taking for granted- so clouds, wind, birds, trees for example are all pretty awe inspiring.
Podcasts. Funny ones, educational ones and kind ones.
Books and audiobooks.
Talking to a non judgemental, kind friend who is able to really listen.
Cold water swimming is, for me, a reliable and remarkable way to boost my mood and make difficult stuff seem somehow more bearable.
Gratitude- not a Pollyanna style spin on things that are genuinely rubbish. More a mindset of noticing that there are things I'm grateful for every single day. No matter how shit that day is!
The serenity prayer, (but without the 'Lord' bit as I don't have a faith), I come back to it again and again and find it incredibly helpful.
Nudging myself to be mindful that I'm a tiny, insignificant being. Things like seeing the sea, the stars and remembering how long the earth has been hosting life compared to how long humans have existed help me to remember this.
Knowing from age and life experience that the phrase "this too shall pass" is very true. I may not know when something will pass, but so far, without fail, everything has eventually and gradually become more easy to manage over time.
Choosing the company of non-judgemental, kind people who love me as I am, warts and all. Similarly, avoiding people who judge, criticise and need me to be someone else.
My cat and dog. One hates me, one adores me. They are very precious.
Knowing that change and loss are an inevitable part of life. I guess this is linked to realising that it's unrealistic to expect to be happy or content all the time.
Allowing myself to feel my feelings rather than trying to avoid them. This one is hard!