A Strapless Bra
What it does: This trusty bra — with wide sides and sewn-in silicone stitching along the edges to keep it in place on your skin — is essential to avoid pesky bra straps peeking out underneath your clothes. Some are even made with a plunging front, for more versatility with skin-baring pieces, or a corseted bottom to provide added support.
When to wear it: You might not wear strapless tops very often, but even for those pieces with thin straps, a strapless bra is essential.
When to replace it: Although it depends on frequency of wear, it's a good idea to pick up a new one at the start of every Summer, when you are sure to start wearing it a lot more often and will need one poised to perform at its best.