I think a number of tobaccos go without saying. Most of us will try 1Q, Carter Hall, Nightcap, and Prince Albert when and where available. So I'd tend to suggest blends or single-leaf a little further out. These aren't required "likes." Some won't like any of them. But they might not try them otherwise.
Tobac-Manil Semois, both the thick cut and the medium cut.
Nat Sherman's 536, their refined subtle but complex English, in either tin or bulk (from the store)
PC Midtown series Chestnut, a pouch or tub tobacco, blended by Russ O. after the classic but discontinued Walnut, non-aro
GLP Triple Play, a plug tobacco in a tin, hearty and sophisticated
C&D Billy Budd, a popular favorite but missed by many, with cigar leaf (but doesn't taste like a cigar in particular)
I don't think there are any "required" blends. This is the golden age of tobacco blending (and single leaf offerings) ...as near as I can tell, so selection is an adventure, and your all-time favorite may not be particularly popular with the pipe tobacco market. The glory is, you can either buy, or mix, the blend that's nearly your ideal, and adjust or change this at will.