Keeping small delicate items dry whilst transporting them through sumps can be done using a variety of containers.
Common small items that might be useful are: Spare batteries for lighting, disto’s, small cameras, or maybe some cigarettes and a lighter !
Inside ones drysuit might be the easiest option (if worn) though lithium batteries inside a suit under pressure might not be best idea and the item(s) may become uncomfortable during the dive due to migration and suit squeeze.
I have a few small containers I have successfully used to carry items through shallow sumps, pictured above are two boxes from Inglesport, an old UK400 torch body and a small home made drytube.
The smaller Inglesport box has enough room for a DistoX2 (if foam is removed) or an Olympus TG4 (waterproof itself to 20m) but not much else. This has survived many a dive to 25 m without leaking.
The larger Inglesport box I have has more room inside than the yellow one, I can fit the disto, an old android phone used for surveying, tipex and a few other small items quite easily inside, this has also done a few dives to 25 m without issue.
For deeper dives I prefer to use my old UK400 torch body, i’m not sure of the exact maximum depth rating of these torches but this one in particular has been to 50 m without issues many times in its previous life as a torch and would likely go deeper, there is the larger version the UK 800 if more space is needed. Its downside is the odd shape though the handle could be cut off to make it smaller if required.
The other item in the photo at the top is a small dry tube I made, it is untested below 25 m and has a larger capacity than the boxes or torch, I used it Mexico to take some dry clothes (merino wool leggings and trouser just about fit in it) through a sump to sleep in whilst camping. Both lids seal with barrel o rings and a large snoopy loop holds the lids in place, once underwater the pressure holds the lids in place.
Small containers like these do have a small amount of bouyancy but this can be offset with rocks or just ignored.