Per John B.:
when I open a sealed tube, in the kit on the bike, I
replace it with another sealed one as find the glue has dried up is
not quite so much of a catastrophe at home

Ever since I opened a virgin, unopened tube (at home, thankfully) and
found it had dried up, I write the purchase date on each tube and carry
at least two unopened tubes in my patch kit.

Probably wretched excess, since I always carry at least one spare inner
tube - and sometimes two...
--
Pete Cresswell