Now it’s too late I’ll add a further recommendation for the Flapjack.
Been using mine pretty much for OP’s stated uses (and it’ll take a 17″ laptop) for most of this year at least.
Seems to be weatherproof (in the highlands), and not showing any obvious signs of wear (or use really).
Before the FJ I had an Osprey Tallon 22 rucksack which I pretty much used for everything commuting, walking, sport climbing, shopping which lasted a good five years before being retired on knackered zip and generally being worn out. So reckon this one will last too. 😀