Underslung tool bags...

[PaulSB]

If you want to protect the frame, helicopter tape under the straps but I'd be worried about the quality of the paint work if it gets damaged by some Velcro straps?

I’m always surprised by the amount of damage to paintwork cable rub can cause.

 

[alecstilleyedye]

bottle cage toolbag in the second bottle cage is both aero and not likely to damage the paint…

 

[brucers]

Carry you bits in a back sack....neither issue applies then.

 

[Adunwoody]

Walking home because you've had a mechanical and have no tools or spares, now that's a drag.

Ba Dum Cha! I enjoyed that one haha

 

[froze]

Yeah like others said you should have gotten a seat bag instead, aero isn't the issue the seat bag just looks cleaner and it's what most cyclists do with their repair gear. But don't throw the bag away, keep it in case you ever decide to get a touring bike, or someday you go for a 100 mile ride you will have a bag to small essential stuff in like a phone and/or snacks.

 

[Ming the Merciless]

The drag will slow you down by 0.00000000001mph. Ask yourself and your mate is that worth it?