Don’t check things that are super-valuable, forget theft an airline can lose your luggage. You can insure your valuables separately. Remember that for international flights checked bag liability is limited under the Montreal Convention.
Of course putting items in your carry on bag, above you in the overhead, can also entail risk especially on long haul flights when everyone in the cabin goes to sleep but there’s still less risk. You can keep truly valuable items with you, under your seat, or at least concealed.