As other people said, I'd go with a topbox for heavy bike-related objects but I'd also put a breakdown kit in the box, it will save you a lot of stress and money at some point in your life, plus having a couple wrenches to adjust your chain always already where you need them is quite neat.
for other generic objects I may want to carry like work related stuff I go with generic ebay assault style backpack: cheap, decently built and the boxy profile is great for when you need to go on a plane since it maximizes volume for the bulk you have to carry, although I'd cut to length and sew all the straps over so they won't flap around and get tangled anywhere. The external webbing would let you install a mounting point for your laptop satchel so you can conveniently carry everything without the weight shifting around, the modifications should take 30mins if you've never picked up a needle and thread in your life.
Maybe you can also mount knockoff pelican cases to your bike, superior protection and versatility compared to aftermarket panniers and could go on with a topbox and backpack.
