Here are three ways I have come up with to carry stuff back and forth to work. I post them here because I think they are a good start, but also know that there are probably better ways. So if you have suggestions on improvements or alternatives, I'd love to hear them, since I employ these every day, and am always looking for ways to improve efficiency, security, coolness, or durability.
Hack #1 is how I carry my U-lock--velcro'd to the rack under the trunk bag. The two back straps on the trunk bag also secure the lock to the rack. It seems like it's not going anywhere. Ways to improve it: I don't know, it seems pretty good to me.
Hack #2 is how I deal with the egregious uselessness of the blinkie loop supplied on the rear of the trunk bag. Clip a blinkie to it, and it points approximately DOWN. Very effective if you want to illuminate the pavement just behind your wheel with attractive flashing light, but not for alerting cars behind you to your presence. So I took a small block of foam, and bent some paperclips to affix it to the bottom of the blinkie clip. The blinkie now points to the rear, and also comes off with the trunk bag. Ways to improve it: a blinkie attached directly to the rack just feels better to me, except for not being able to take it with me when I park the bike. Some minor sewing could probably make the blinkie loop actually functional as a blinkie loop. But I kind of like the block of foam hack in that it clearly points out the utter incompetence of either the designer or implementer or both of this loop, while also illustrating my personal intolerance of same.
Hack #3 is just one example of how I am using Velcro One-wrap, which brought a huge smile to my face when I saw that it comes in multi-foot rolls. I wanted to attach my Topeak Mountain Morph pump somewhere that goes with me when I park the bike. It's too big to fit inside the current trunk bag, but that's one of it's features: its size, along with its small built-in hose, make it my favorite way to get air into the tire on the go. I have several other portable pumps that are smaller, and they all do an adequate job, but the Mountain Morph just defeats them all. A couple of wraps of One-wrap through D-rings, along with a backup safety wire attachment, and I'm set. Ways to improve it: you can't see it in the picture, but this position is not ideal in that the other end of the pump can work its way forward into the area of the back of the saddle. It doesn't hurt or anything, and it's easily resolved with a gentle push back, but there must be better places to mount the pump such that it still easily goes with me when I lock up the bike. The supplied bracket doesn't qualify, since it means I would have to detach, carry, and reattach the pump separately, and I don't want one more object like that. I think a couple of D-rings sewed onto the trunk bag, one in the area directly below the "3" and above the current Velcro loop strip, would be an improvement. I may give that a shot. Any other suggestions? Get up. Go ride.