Gratuity for Catering Company, Rentals Included

I would say that it should just be on food and service. Feel free to write up your own little cost + gratuity and email them it so that they know where you are wanting the tip to be and on what so that it isn't awkward when you question your own tip to them.

They should include it in the pricing

Gratuity is either added or not added to some of the vendor costs. Our venue had gratuity charge applied to our fees and didn't give anything else on top.

You added the gratuity charge which saves you the tip on top to give since they have that amount paid by you on top of their services paid. Its nice to do so avoiding additional costs.

You shouldnt be paying gratuity on rental technically.. But it may be hard for them to break it all down. My venue added 18% gratuity onto our cost which was mainly just food. If it's not too late it might be easier for you to figure out the total cost of food and service and figure out too from that.