A pub and brewery in town does a delicious porter with caramel and coffee tones. What particular ingredients do I need to add to my mash to achieve this?
Black malt and Roasted Barley will deliver coffee notes. Using anywhere from 0.5lb up to 1lb of either (or in combination) per 5 gallon batch is the norm. Caramel notes are easily delivered from crystal/caramel malts. I have used a full pound of Crystal 60L in a brown ale and it had a real nice toffee/caramel punch to it. Using less than a pound of caramel or crystal malts is the norm per 5 gallon batch. Crystal malts come in a range of color/flavor values. Try a mix of C60 and C40, or a combination of C60 and C80 for more of a darker fruit flavor.
I also find that black malt with crystal malt is the best way to get coffee tones. As black malt alone tends to just taste like heavy roast. The crystal character really helps carry the flavors to a nice place.
Im not sure how much coffee flavor youre going for, but Ive been reading a lot (mostly on stack exchange) about making beer with coffee. You could cold press some coffee and add it at bottling. Another suggestion Ive read which I plan on trying this week is to "dry hop" during primary or secondary fermentation with some coursely ground beans in a muslin bag.