I have one favor to ask; if you have several questions in the future, please split them into three threads. Otherwise, it is difficult to read for others since this forum doesn’t allow to branch out threads. Thanks for considering.
#1 Fishing pole. I’m a big fan of manual animation, of course. Which, in this case, would mean Joints. Perhaps run via PoseMorph.
While the fish pulls, the fisher might have a reaction, pulling against it. I think with just one slider, you can create a nice expression, while there is no limitation to add different ones to the Pose Morph.
Yes, I know; typically, most people like to do it with Dynamics, and with all that complexity, they might lose touch with the expression. Joints can have dynamics, but one gives up a little bit of art directing with this, not always, but the PoseMorph gives you a lot of control.
#2 Fish in the bag. I could go here with a model of the clear bag and have a Jiggle Deformer working on it. Perhaps harvesting some key poses and use as well PoseMorph with those.
Having talked against Dynamics above, I could see it here for the surface as an excellent option, but again, you give up a little bit of control, art-directing, and whatnot. But have a look.
#3 Pulling trousers. If I understand this correctly, the trousers are more or less close to the legs.
Here are two options: low tech, which means we blend from one into the other and then crumble it. [01
Or we use Cloth and create a collider with the Volume Object 
Enjoy your project