I'll give you (at least) two- one from when I was a teenager, and didn't have anything else, and one from today when I made it past being a teenager and learned I have everything else.
The first is what my mother once told me offhand, but that lodged between my ribs and stayed there ever since: "you can always die later, but you can't always come back." I was kept alive at least twice by the question "what will I miss if I cannot come back for it?" And in those moments, it was a genuine comfort to me to understand that this all ends anyway at some point, and there's really no sense in going home early, but the question also made me stop and think long enough to find something I didn't want to miss out on because I can't come back to this level once I'm out. At the time, it was any number of things, but largely "I want to go scuba diving on the great barrier reef someday and I can't do that if I'm dead so I guess I'll keep going" (and FYI several years later, I actually made it to Australia from Michigan, USA, and went scuba diving on the great barrier reef, and it was every bit as amazing as I had hoped and it was 110% worth staying for, so feel free to want lofty things).
Today, 20+ years later, I don't have to stop to think that hard anymore, because so many of the seeds I planted between then and now, of things I don't want to miss, are growing beautifully. I have stories I want to finish writing, I have stories I want to finish consuming (reading, viewing, hearing about etc). I have art I want to make and art I want to see, places I still want to visit, events I want to go to, structures and animals I want to see in person. I have animals to take care of - my pets, and also the family of crows in my yard that visits and trades me feathers for leftovers and the woodland creatures (insects, birds, squirrels the groundhog under the mulberry tree, the doe that visits with two fawns in the afternoon, the turkeys that bring their gaggle of poults by in the fall every year) that visit my yard because I have rewilded much of it and take care to help preserve their areas for them - and a partner I promised not to leave. I have friends that I want to see who want to see me, and who might need my help sometime so I can't just abandon them. I have folks online looking forward to seeing the next silly little photo of my birds, and there's no way to know when someone just needs a silly little photo of a bird to remember there are good things in this world worth sticking around for a little longer, so they don't miss the next one.
I want to see Stonehenge in person someday. I want to pet an anteater someday. I want to hold my published book in my hands and cry about it a little. I want to see my nephews and my niece grow up and decide what they want out of life so I can help them get it. I want to see what baby peafowl my birds will make next year. I want to make a wild type celadon coturnix bloodline so I can offer others a clean slate. I want to finish creating the genetics info section of my website so I can share information about peafowl genetics for free and put both middle fingers up at the old white dude gatekeepers who want to keep everyone else dependent on them so they can make $$ off being the only ones who know stuff. I want to see the northern lights in person, up in Alaska or Canada or something where they're more visible. I want to go to the grand canyon. I want to walk in a redwood forest. I want to make a lucky Pokemon trade with my mother so we can get cool shinies.
The thing I've found is that you don't necessarily need a "purpose," to stay. You don't have to be useful, you don't have to have a destiny or a fate or a calling or be needed, and the idea that everyone does was a hindrance in my early life, because I didn't feel like the world needed my presence, or that I was ever going to do enough to fulfill a purpose. Turns out it doesn't matter if the world needs me or doesn't need me, because that's not what it's about for me. Life doesn't have to be about doing anything useful or meaningful in a greater scheme or even lasting, because it's not a job we're doing. There's no requirement for doing an amount of things or doing great things. It's a party we're at, it's an event we're attending, it's a movie we're watching, it is a story we're living. Of course it has an end, but there's simply no sense skipping to it early- we'll miss the good bits in the middle, even if we don't know what those are or will be, yet.
I might see a cool bird. I might find a pretty rock. I might see a weird cloud. I might find a new favorite fanfic. I might have a new story idea. I might eat the best nectarine I've ever had. I might bake the perfect batch of cookies. I might be outside on a warm day and feel the pleasant touch of a cool breeze. I might see a perfectly clean paperclip on a dusty dirty floor and be struck by how pretty it is when it glints in the sun. I don't know! I don't know what I will experience next but I know I want to find out and I know I can't find out if I'm not here for it. I know I am alive because that is what I needed (and continue to need) to be, to find out what I want next, to find out what thing I will experience next.