Make a story about a kangaroo and a Tasmanian devil. But not just any kangaroo and Tasmanian devil.
Alright, so your main setting should be in Australia since that's where kangaroos and Tasmanian devil live. Let's say something happened to Kangaroo. There was a deal between him and a dingo. Dingo demanded rabbits, rodents, birds, and/or lizards to eat for supper and would give Kangaroo something stylish in return. But since Kangaroo was a herbivore, he refused. Of course, Dingo got angry and told Kangaroo that if he didn't have any supper for Dingo by dawn, he would eat him.
Kangaroo, of course, couldn't do this alone. That's why he asked the Tasmanian devil if he could help. But what if this had a twist? What if the Tasmanian wasn't Kangaroo's friend, but instead, an enemy, perhaps?
Of course, Tasmanian would be skeptical. Why would an old enemy ask him for a favor? Kangaroo then explains and Tasmanian could offer to help. Soon, throughout a journey, you will see a bond start to form between Kangaroo and Tasmanian. Kangaroo teaches Tasmanian what he knows and vice versa.
Soon, when they spot a rabbit, it was Tasmanian's time to shine. But, this story needs some sort of conflict. What will happen if Tasmanian betrayed Kangaroo?
Maybe Tasmanian sneaks away and Kangaroo has no other choice but to get the rabbit. However, Kangaroo's style of thinking is different. He wants to find a way to make sure Dingo gets supper but also get his revenge on Tasmanian. Where does the story go beyond this point? It's now up to you.
This is just an idea, so feel free to edit out parts you want or add on parts you want.
I doubt you'll get many real ideas, other than maybe grapefruit, and I'm definitely not giving away any of my oh-so-valuable ideas. In any case, this advice will help you in the future.
If you really want ideas, just read a good book or watch a good movie, or hell, play one of the many storygames on this very site. Don't plagiarize, just see if there's anything particularly interesting: maybe a side plot that leaves you with questions, maybe you just really like the structure and want to write something in that style. Maybe you look the idea but not the execution (perfect opportunity in that case). If that's still not enough, just go for a walk around the block/neighborhood/pocket dimension, and just look. Look for anything and everything. Maybe you see a really beautiful sunset or tree, or some sort of scene in a public space. Maybe you just see a really interesting-looking person and decide to write about them. And if all that is still not enough, just write as much as possible about something in your room. A lamp, a textbook, and even a random cookie crumb is a viable subject. Just write something, anything. I myself have really struggled with writer's block, and these are the various ways I've dealt with it.
I was right, he IS trying to steal my precious ideas!
Please don't kill me. :[
Come up with your own idea. Jesus tap dancing Christ, this is the easiest part of a fucking story. I have ideas every time I take a shit. I have ideas when I go for long aimless drives because there's no where to go and nothing to do but think of fucking storygame ideas. Good lord.
If you can't come up with your own idea, you shouldn't be writing anything; you should be turned into some kind of a beast of burden, and forced to push a giant wheel around all goddamn day.