I always tend to forget something major when I travel. From bathing suits to razor blades, it's always something. This usually resulted in a last-minute trip to whatever convenience store or clothing shop. And when I would get home, I would unpack everything, including said items, only to forget them a second time around.
Around the second bathing suit, I decided enough was enough. When I could actually remember, I packed up the extra razor, (one of the) extra bathing suits, etc, etc, in the suitcase I always use. They don't get used unless I'm traveling, but I'm guaranteed to have the essentials. No more running around trying to find a strapless bra or deodorant!