You can store anything that has been lawfully acquired by you. It does not need to belong to you but you should have the right to access it and store it in your locker. This can be cash, jewellery, property deeds, legal documents, wills, rare coins, share certificates, back up disks, insurance contract, etc. You are not permitted to store anything illegal or dangerous like drugs, weapons, explosives, gas canisters, or liquids of any kind. You are also not permitted to store anything that has not been legally acquired by you.