For me
Baitfish: bluegill, yellow perch, golden shiners, shiners...
Other: Craws, newts, frogs, mice...
And of course the bird
In my opinion the most important to imitate (for me in my area atleast), is a craw, or a bluegill... You can do so with crankbaits, texas rigs, swim jigs, jigs, etc. You can imitate the craw with even more ways than the bluegill or perch with a carolina rig or jika rig.
Your right, forage is going to be more abundant at certain times and the bass are going to be targeting certain things more than others at times. This calls for different techniques and knowing where the forage will be. For example, imitating a bluegill or a craw prespawn will be different than postspawn or even spawn. Speed, size, location, and movement will be different...
If I were you I'd get a solid hold on imitating craws, and for a baitfish bluegill/perch, as I said above, you can imitate them similarly in many situations...