Senkos flyine,
finesse jigs,
anything you can hang (nose hook) on a drop shot hook like a creature bait flyline.
drop shot
wacky jighead
scrounger
light t-rig
fine wire shakey head
jerkin' small flukes
flyline robos far
nailed robos
split shot
darter
etc etc etc
It's gonna boil down to the hook you want to use, and weather or not your rod will snap if it lugs a 16" worm on 4lb test. lol
Again, use light wire hooks on 4lb.
Thicker hooks will require rods with more backbone and therefore thicker line.
A spinnerbait is not a good 4lb line bait.
Neither is a Superline gamakatsu EWG hook.
When you start reaching baits 1/4oz or more, you'll probably need thicker than 4lb line also.
A few long casts with 4lb line and a 1/4oz sinker t-rig and you will cast the rig off with a loud whip snap.
Keep in mind adding a worm to a 1/4oz sinker T-rig increases the weight quite a bit.