Tidale Stromgurd:
If without my gear I'm a +8 to swim already and I breathe water. Others might want a dive suit but I had better be okay.
I totally forgot that my armor counts as light armor. I paid a lot to make it count as light so yeah I'm going to get the diving suit and wear it over my armor if you'll allow that.
Sure, just making sure everyone has clothes, you won't always be fighting. I always recommend picking up a kit or two.
Folding poles, pitons and hammers, rope, folding boat, etc, well, even a Kit, Diver's would be good
https://www.d20pfsrd.com/equip...its/#TOC-Kit-Diver-s
Common adventuring goodies, a crowbar, etc.
Even chalk is good for marking the way.
Pitons are great for when you can't remove a door for whatever reason and think it might close behind you to force an encounter, you can hammer pitons down to prevent it from closing. Using a crowbar to remove the pins and pull the entire door off, or remove a door elsewhere to throw down to wedge a door open.
Block and tackle are great for making rope bridges, or pulling party members up and down in a make-shift elevator, or moving heavy goodies, or ripping off entire sections of wall, even using it to bind down huge critters. Maybe those statues you spot look extra suspicious, so you block them all down with rope and tackle, tightening them so they can't move if they actually are golems or other things.
That, or just using rope to haul up buddies that fall into a pit.