What do you use to fill space on your island?

I've been playing off and on for around 4 years now, I've reset my island a couple times in the process. But I've never actually *completed* an island.

I usually get off to a good start, have some good ideas and end up with a few finished spots on my island, but then I run out of inspiration and I'm left with *so much* empty space, and no idea how to fill it. I also feel like there's never enough furniture/items for me to fill spaces adequately. I see other people's gorgeous islands that are crammed full of stuff, and mine looks naked by comparison.

What's your go-to for filling space and making an island look complete?