There really is no way to answer your question but I will try to give you a bit of guidance.

The two main factors are length of trip, and your body. You want to focus on the length of your torso. A proper pack should comfortably wrap around the upper part of your hips to shift the weight into your legs and off of your back and torso (this is the absolute most important thing). You should really try on multiple packs at a store. Osprey packs are my hiking preference because their hip belts are made to be custom formed to you after you buy it.

Of course, if you are not hiking then it doesn't really matter. Given that you want a bug out bag I would make this the determining factor.

Look for a pack with around 60L (around 3600 in^3) capacity. That can easily fit 3 days of luxury style camping and well over a week of efficiently packed and proper equipment.

I too prefer the MOLLE systems mostly due to their adaptability and from using it in the Corps.

My personal preference is also to find a pack made from no less than 600 denier; the closer you get to 840D the better for durability. I would never drop below 400 though since you want the whole bug out option.

Hope that helps point you in the right direction.

One last thing....it will be very hard to get a pack that is going to last for $125 while dual hatting bug out and Yosemite level hiking. Some people will disagree and I am only stating my opinion on this and I really do not know how far into Yosemite you are going to be going so I am only speculating. Look on craigslist in the CA,WY,UT, and CO states. There are many more hikers out there and you can get a steal if you can build up enough trust to do the shipping thing.