What to take on a hike?

What to take on a hike, for one day?
I'm planning a small hike in the mountains. 
They say you can take very few things, but I don't believe it.
The backpack is about 25 liters.
The list of things I plan to take:
1) water (1 liter) and food.
2) stabilizer for smartphone and power bank.
3) raincoat and insulated vest.
In fact, nothing else fits)))))) 
Question to connoisseurs, - what things are still necessary for a small hike?

First aid /A topo map and trusty compass/ Food and hydration and finally hiking boots these are the most important things.

Besides the things you've already listed, I'd also recommend bringing a first aid kit, including bandages, alcohol wipes, and tweezers in case of a minor injury. A map and compass (or GPS) can also be useful in case you get lost. And don't forget the sunscreen and hat, since you'll be outdoors all day. Depending on the terrain and length of your hike, trekking poles and hiking shoes with good ankle support can be a big help. Finally, you might want to bring a camera to capture the scenery and document your adventure.

Depending on the hike's difficulty, you may need trekking poles, a camera, or a field guide.