First off welcome .

You can always bungee your backpack to your rear rack. It takes the weight off of you and onto the bike. I did this until I put a milk crate on the back of my bike so I can just throw my backpack in it without strapping it down. I can also use it for grocery shopping.

My suggestions would be fenders, a good lock, and puncture resistant tires. you can also throw your flat repair kit in an unused water bottle.