On our trailers we put all things that our Biketour group needs and cannot be distributed by the participants: Some food, cooking pots, stoves, flyers and other equipment. They can load up to 35kg. We take turns to carry them and everybody can do it, if you want you can also share it for a day with someone else and change half-way.
The Biketour owns two bob-trailers who have only one wheel. Thus they are slimmer but not as stable as 2-wheel trailers. They are fixed with a quick-release skewer, so in order to be able to pull them you need to have such an axle on your back wheel.
In previous years the biketour also often had a borrowed two-wheel trailer, we are trying to get one again for this year, maybe the one we had last year, which was very easy to mount, also on bicycles with nuts and not quick release and lightweight to ride.
The most important thing to keep in mind for safe cycling with a trailer is the stability - pack the weight as low as possible and ride carefully, especially downhill and in curves - the trailers don't have brakes and their weight can get you off-balance. Let someone show you how to securely attach the trailer to your bicycle including the security pins.