By items do you mean items to boost your strength or for designated item bars (eg main bar on haunting)
Using items on item bars in any epic battles will make your end plunder higher. I hope this answered your question!
There are different Blood Rains epic battles. The one you're doing is called "The Depraved - Blood Rains". But currently there's also one called "Desert Sting - Blood Rains".The Blood Rains epic battles change every 2 days. And yes, you're correct. The item Sleeping Potion is used in The Depraved.