Get some air curing putty that can adhere to this plastic in question. Or modify the idea with just glue and piece of some other thing.
If you happen to be used to wrap your multimeter into rubberband as I do then a piece of string can help even more. Or if you don't you can also start doing the wrapping thing now :)
Step 1: Put the Two Small Ones Together to Form Bigger Thing
For even better lostproofness make a hole into this combined cap.
Step 2: Put a Leash Onto Them
If you use the rubberband or just got talked into using it then put the string around rubberband and you will have all accesories together - just one sheep to keep an eye on.
Live the rest of your life with peace of mind.