How Do You Carry Everything?

I only need to carry my lunch into work usually. My church is right next to where I work so, Sunday mornings I drop off a backpack full of clean clothes to last me the week and just leave it at work. I'm an electrician and as such I need a water jug, too. It works out really well. In the summer time I have an active mini-fridge that I can keep fruit, drinks, and ice packs in.
 I know other people use full racks and pannier setups. I'm glad I don't need all that. I just have a single rear rack that attaches to the seatpost of my bike. It's another hand me down from my wife's grandfather. It's plastic, and has a tiny storage spot for tire levers and a patch kit. It works and I've never had a desire to upgrade it.
 When I first started commuting to work, I used a backpack. After a while that just hurts. I have poor posture and that certainly didn't help any.
I've had different lunch box configurations over the last three years. The hardshell Igloos and the softshell Igloos. Right now I'm using a bike specific one from Avenir that I love. It's not fully waterproof though so I'll wrap it in a grocery bag if it's a raining pretty hard. I've fit a full wardrobe plus my lunch in this thing before. It's perfect for those days that are freezing in the morning but, 40s or 50s  during the right home. You can stuff your outerwear in it and not have to worry about it.  Look out how big this thing extends...{That's what she said}

This is a shot with the Thermos in the bag.

Compact mode.

It has a pocket on the outside for a water bottle. I use that for my headlight battery and hook my keys on the loop that's there. I also keep a multi-tool, spare tube,wallet, and phone all on the outer pockets. I could even have my pump strapped to it but, that's on the bike frame. It is a complete softshell. I took a hard plastic liner from another lunchbox and use that inside to keep my lunch together. The insulation isn't as thick as a normal lunch box. I'm not quite sure how it'll hold up all day sitting in a hot truck in the summer. I'll probably bring a cooler to work and transfer my lunch over in the summer. The three velcro straps hold it tight to the rack. I've never had it so much as move and I have hit some pretty serious potholes up here in the northeast.

It's got a trendy messenger bag type strap for carrying it and an assortment of loops for attaching random stuff to.

Avenir Excursion Rack-Top Bag (830 Cubic Inches)