I like X's inclusion of your items. Add your familiar to the clause if you have one and he's on your person.
Remember, the key thing is to use invisibility as your clause, because anything that you want to trigger the contingency also would cancel an invisibility. Make sure you specify that invisibility doesn't actually have to be cast to use it. So anything that happens to you that, if used by a person (thus including traps in the contingency), would negate their real or theoretical invisibility spell will trigger your contingency.