Item help!!

So basically I needed to know some good items to put on gengar and rotom because I was just gonna have leftovers but I wanna mix it up a bit also can anyone suggest a good pokemon to have to remove spikes and stealth rocks prefarebly one that can learn fire moves

You can use chesto resto on Rotom. Although it's common it's effective and something other than leftovers. Scarf trick is also a thing for Rotom.
For Gengar a choice scarf or focus sash destiny bond are useful.

For hazard removal and fire type attack: Torkoal learns rapid spin and is a fire type so it can learn those moves, Starmie and Blastoise also learn rapid spin and you could give them hidden power fire and (Mega) Charizard, Zapdos, Crobat, (Mega) Pidgeot, Togekiss, Honchkrow, Salamence and Archeops all learn defog and some kind of fire move. Latios and Latias also learn defog and hidden power fire.

thanks ill probably use charizard i just wanted a fire type because i struggle eith grass types

If you already have a mega maybe an other pokémon is better. Charizard without mega evolution is not good.