I have a list of buyers who purchased diet pills and would like sell another product to them and hit them with CCPC.
Any suggestions on other products that they this demographic would likely buy?
Thanks
CCPC?
Do you have any info on the demographic, e.g. Country, Gender, etc.?
If they bought diet pills then hell, they can probably be marketed anything. Perhaps you should invest some time in designing a mailing campaign that builds trust and then pitches products to them later on? A bit outside my area of knowledge but there are some email fiends in here, I'm sure they'll give you some ideas.
I get hit up all the time for this type of data. You can work out agreements with data brokers who love these type of subprime lists.
Any good guides I can follow?
Given it's diet stuff, the obvious thing would be diet tips - probably "low effort" tips given they bought pills. Send them a few content - heavy, no sales emails, and then you can pitch a product, then more content emails, repeat 
If you don't want to write the content this is the sorry of thing it's very possible to outsource - find a good diet blogger and offer to pay them to ghost write for you.
OR ...
you could take a lot of the free content that guys like me and guys like Mike Geary put out to our affiliates (content = helpful articles one how to eat healthier, etc) and then that stuff gives them good content and soft sells our products to them making you money on the backend and making your email list happy.
The other way to do it is to go to a broker -- give them your data -- or setup a deal where they sell your data to people who rent lists, etc and they will make you money off of blasting the crap out of your list (I've never done this but I know guys who have -- churn and burn is not my style since I care about my customers and want to add value but that's what a lot of guys do to monetize data on the backend).