Shoes, spare spring set, magnet and misc...depends on which trailer I'm borrowing...
I don't own a trailer anymore and borrow...but first time make a deal for them
to allow me to check it out and repair/adjust/etc
Whenever it needs trailer shoes, I buy two sets and then setup their 'kit'
Use 5 gallon plastic paint buckets for lots of these kinds of things
From snow chains, to trailer brake kit, etc
Plastic lid that serves as a seat/stool. Canvas pouch that fits over the bucket
lip and has pockets on the inside portion and outside portion
Plastic bags holes the box with shoes. Ditto plastic for the spring kit. Magnets.
Zip ties. Gloves. High temp lube. Brake shoe tool. Bungee Cords. ETC
Started when I was a partner in a +8K lb boat. Used to leave it with the trailer
but the partners never replaced anything...nor told me they used the parts. Some
times on their other trailers
It is water tight. Keeps everything in one place...even after moving it around
several times during a trip.
One of the first things I check for when borrowing...some times find that they
used the parts and/or 'loaned' parts to others during their trip. Then check the
other stuff am anal about