You must buy each of the powerups from the shop at least once throughout all your playthroughs.
The Powerups you can buy are:
Catnip
Defibrillator
Extra Time
Gas Mask
Heartbeat Sensor
Holy Water
Large Water Tank
Magnifying Glass
Max Health
Remote Water Bombs
Speed Boots
Spiked Boots
Super Axe
Super Extinguisher
Super Hose
Thermal Goggles
Water Bombs
The best way I found to get this if it doesn't come naturally is to load up the Factory levels. There is a shop within 4-1. I would head straight for the shop, ignoring most of the fire and see if they had what I needed. If they didn't I would die and try again, if they did then I would head in to the level to make the required cash. Do not put out all of the fire as you can stand in the room and it will spread again so you can get more cash from it.
I made a video of my final purchase. I aimed to make the video longer, but got lucky and found my final item on recording time: