More random tidbits: You'd semi-obviously want a sacrificial wrap over the mask if you're painting, as well as few spare cartridges. There are particulate filters that are just regular paper masks, organic vapor cans for painting, and couple of acid cans for toxic gases. DYOR and use the right one for the task. Particulate filters go on top of gas cans on the iconic 3M 6000 series masks; it's not integrated to the can. The cans also technically only last few hours after opening the package, so technically you should be replacing twice daily. They also can't protect against large amounts of toxic substances like videogame thick green vapors of alien weapons, only what's somewhat casually filtered. In e.g. inside an active volcano, go for full scuba or something that don't rely on filtering. The reason why some masks use pair of cans as opposed to one can, is just for easier breathing. The performance on paper is the same; you can seal off one port with something if you want. The improvement is maybe not negligible, but you get used to breathing through masks quickly anyway. The mini mask that covers mouth and nose inside a full face mask exists to help clear condensation by forcing you to breathe in fresh air around its front surface and force exhalation through the exhaust valve. Removing it will steam up the shield. The air drawn in is filtered, but exhaust is not; if the wearer is infected with something, the mask won't help stop the spread.
TL;DR: gas masks is its own mini rabbit hole.