It is important to remember what not to store.
Do not store anything that is highly flammable (e.g., oxidizers, gasses, etc.), environmentally hazardous, perishable (like food – it happens), or anything that is a risk to others’ property. Some examples include paints, batteries, gasoline, oils, paint thinner or solvents, volatile cleaning products, chlorine, or acids.
Don’t store plants, animals, or anything perishable.
Don’t store hazardous liquids, explosives, or ammunition.
Remember that liquids may freeze when they are outside in your mobile storage container (our warehouse is heated, so no problem there). If they freeze when outside (e.g., during packing, pick-up, delivery, or unloading), they may break the container they are in and then leak when they thaw.
DO NOT store things that are simply irreplaceable. Family heirlooms, jewelry, cash, bonds, stock certificates, and other valuables belong in a safe-deposit box at your bank. Your insurance will likely not cover these items at their value to you, so particular care should be taken here.
Finally, don’t store anything illegal. The police can cut the lock off your container and get in.