Float Tube Pumps & Gauges
The air chambers on floatation craft should be fully inflated to keep you properly afloat. If you air up properly before launching you should be able to ride high and dry all day. However, there are times and circumstances in which your air chamber(s) will shrink and you will want to restore them to a full and rigid condition. Cold air or cold water can cause air chamber shrinkage. A quick top off will restore them for the rest of the day. Pinhole leaks and punctures are worse because you have to keep adding air until you can repair the leak. Having an air pump on board makes it easier to address air loss without having to stop fishing and return to your vehicle.
Some tubers and tooners purchase small air pumps (and extra connectors) for the express purpose of being able to carry them out on their craft. Of course you hope you never have to use them. If you do need to add air you will be happy you sacrificed some valuable space to accommodate that pump.