I'd get pissed but since it's a family member, I'll probably just get over it but he/she will never have access to any stuff I own from then on. I'd probably just be civil but they he/she would never get any favors/help from me until I have really forgiven/forgotten what had happened.

If it was someone close, he/she have to make up for it big time or at least pay for the cost of the items or try to replace them.