Im not sure what insurance you may need other than your public liability but it would be extremenly wise to cover your back by adding a disclaimer to your terms and conditions in the event of somebody claiming loss or damage.
something on the lines of, " The client shall ensure that all valubles are stored away when work is carried out. The company will not be responsible for the clients failure to comply with this obligation."
simple but to the point..
p.s you may want to fill in some more details on your profile like location etc and you may get some more replys.
Regards
Dave