What's a useful, but simple skill to learn?

CPR
heimlich manuever

cooking,self defense,sewing,writing and being kind to other people and animals.If you're nice to others,they'll be nice to you.

Cooking. Some can be complicated, some can be simple, but some level of cooking is almost necessary.

Funny answer: Bitchcraft
Serious answer: Small acts of kindness daily.

lying-I'm not saying it's a good thing but let's face it, it's useful

cooking-start basic and work upwards, learn enough that Ты could feed yourself so Ты don't have to go out and eat.

sewing-start basic and work upwards, knowing how to sew on buttons and patch things up is especially useful

CPR

Use a compass/how to read a map

make a campfire

make a shelter

Heimlich

Ride a bike

Budget money and/or time

Learn basic words in a foreign language (Hello, where's the bathroom, etc.)

How to compliment, apologize, change the subject, act polite, express condolences, etc. communicate properly even if Ты don't mean it.

how to tie a tie

Swim-enough to stay afloat/tread water

Public speaking

Basically, always be prepared.

Knitting, Sewing, Writing, Reading, Cooking, Gardening, Cutting your own hair, Swimming

Cooking!

Walking quietly. Ты never know when Ты will need to sneak up on someone.

Prussia
Germany
And Lithuania and there history <3