3800 series engine, N/A. Noticed some dryed up coolant under the oil cap and am going to change the gasket. I'm trying to put together a parts list so I can get it done.

I am going to change spark plugs while I'm down there.
I need to change the coolant also correct?
The gasket itself
Sealant for the gasket - Recommendation??
Going to change the oil again. (Did it about 1,000 miles ago) So 5qt oil and a filter.

Is there anything else little that I need?

This should answer your questions. If anything was missed, just ask.

https://www.gmforum.com/t278911/

While you are at it. The upper intake manifold has to come off in order to change the gaskets. One of the largest issues with these motors is the upper manifold. By the EGR that passes through it, coolant ports are compromised and dump coolant into the intake tract. Best to change out the manifold while you are doing the gaskets.