Items in infection have quite a lot of potential. We can do quite a lot of things with them. I'll list my ideas for some here, and you can do the same as long as they are balanced cough cheesypoofs cough.
Antidote
I can imagine this as a mainly late game item, like All In. How it would work is you can't use the item regularly. While you still have the item, you can grab an infected and a bar would pop up similar to the infection process, but it cures the infected. I can imagine this being interesting in the game, where instead of running and hiding from the zombies, you actively fight against them. The hunter becomes the hunted.
Sweet Scent
This is an infected only item. When used, the infected gains an aura where anyone within the aura is magnetised towards the user. Of course people in the aura can resist it, and if they have speed boost or invisibility, it just doesn't affect them. This could be used to combat against hard to reach spots and exploits.
Reloader
I think this should be the first item available for both sides. If the user, goodie or infected, grabs a gun while the item is active, the gun will have infinite ammo for as long as the item lasts. Stamina is still a factor in how much it can be used, of course. I think this would be useful for goodies if they're being hunted by a group of infected, and useful for the infected to help get a goodie who just won't stop getting into that stupid out of reach spot.
Decoy
This item will set up a mannequin. When it's in the radius of an infected or the book, it will show up as a goodie on the map. This should be ignored during the hunting hour though. It would be too confusing if there was two spot on the map and only one goodie left.
Garfat's Glasses
Again, an item for the infected. When used, outlines of all the goodies nearby or affected by the book will show up. I just thought it would be easier than trying to look for a dot on a map and it just feels natural for Garfat to have heat detectors in his glasses.
Ghost Tentacles
This one is based on the Factory Crisis sabotage. When used, one of two things can happen. Tentacles burst out when anyone gets close to their hiding spot and knock people away (like in factory crisis except more surprising) or burst out when goodies get close and simply hold them, not letting them move and leaving them as sitting ducks for the infected. The goodies are not notified about the tentacles, though infected are not only notified but also shown the locations, but purifiers (the fire extinguishers from infected) spawn around the map, telling goodies to be on their guard.