First- keep in mind this has to keep you alive for 300 miles. That's a long way to go, on foot that will probably take you the better part of a month to make that trip. It's unlikely that you could carry that much food, and definitely not that much water. So for all intensive purposes, you are preparing for indefinite survival. Given that, I don't think 50lbs is too overweight. I think your biggest problem is you have too small a backpack, and tried to augment it by attaching another bag, and the two are unstable together. I think a larger backpack, something more like a backpacker camping backpack, might be the way to go.

That said, I wouldn't rule out bikes. It's unlikely that the road system will be rendered so inoperable that you couldn't get a bike across. The main reason why you might not want to bike is two-legged predators, but that basically means bushwhacking the entire way which will be MUCH slower. If you can set out on a bike early enough, and you're in good shape, you should be able to make the journey in a week or less so you can arrive before people start running out of things and getting desperate.

Also remember you won't be carrying ALL of this the whole way. For example, you'd probably put on the boots and stow whatever shoes you're wearing. If it's winter you'll be wearing the coat, if spring or summer you might just leave the coat behind.

You have 20 AAA batteries, instead of that many batteries get one of the flexible solar panel battery chargers and some NiMH AAAs. Keep normal alkaline or lithium AAAs in the flashlights, and have one full set of NiMH AAAs plus a few spares. Come up with a way to attach the solar panel to the outside of your pack. That way when you hike during the day it charges the NiMH batteries, just discard the initial AAAs when they're done and start using the NiMHs. That may save a bit of weight (once the alkalines are discarded) but it'll also increase the longevity of your kit to more or less indefinite.

Consider replacing the radio with a BaseCamp two-way. No solar charge (you can use the solar panel mentioned above for that) but it's also a two-way radio, and that's going to be important. Without cell phones, two-way radios are all you'll have.

Dump the Bics and get a good jet torch lighter. Much hotter flame and more wind-resistant, will get your fire going faster and easier in worse conditions. And make sure that magnesium firestarter has a flint so you can make sparks with a knife, so you're not SOL when you run out of butane and matches.

Gun-wise the Takedown is a good choice, I'd also get an optic of some kind to help in hunting small game. Might also want to include some literature on how to prepare small game for eating. On the same thread, snare wire takes up almost no weight/space and can get you some critters. A small fishing kit is another worthwhile addition.

I think the 9mm and some ammo would equally important, for defense against two-legged predators. 300 miles is a long way, people can get desperate. Carry at least 50 rounds of spare ammo, and a concealable holster. Remember, CCW permits may not matter post-collapse but they matter now- many places require a gun to be stored in a 'locked hard-sided container' or something similar. Make sure you have a valid permit wherever you can get one, just in case. Also be aware that Illinois doesn't recognize the right of citizens to bear arms outside the home- they do not offer CCW permits of any kind and legally carrying any sort of gun is difficult or impossible in IL. I say this because during Katrina, police confiscated firearms from travelers.

Bottom line- your best bet is going to be to get on a bike and try to make the trip quickly if possible. If you can get home before people run out of things, you'll be much better off...