Selena Gomez solves the eternal problem of midsection bunchiness by pulling on a pair of cutoffs over her Solid & Striped suit. Side-boob beginners: This one's for you. (Low-cut armholes + stretchy fabric = no shifting.)
Problem: plunge-y jumpsuit and no fashion tape. Solution: any bathing suit top with straps that fit under the romper's. Play with print- and color-clashing, or, if you can, match like this Hoffman ensemble.