If you like to wear Racerback tops and don’t have a decent racerback bra you can make your own with a paperclip.
Here’s how:
Anyway, I hope this helps someone out in a pinch. The paperclip also works great to keep bra straps from slipping off the shoulders too for regular shirts.
You can also use plain dental floss in a pinch, I have one top that is narrow in the front, so I simply tie the bra straps and then use fingernail clippers to snip the knot to help hide the straps.