Unless you are lucky enough to be the host of a table-top game (if lucky is the right word), you understand the drive to pack everything you think you'll need for the game, and the anguish of realizing you've forgotten the One Vital Thing at home. As a GM this is doubly painful because the One Vital Thing is often a section of session notes, or the stats for the vampire queen the party is supposed to confront, and now you're scrambling, improvising and trying to remember what you had written.
One method of solving this problem is to bring everything. I used to bring every sourcebook I owned to every game. And multiple binders of notes. We were all in engineering school, so the hundred-pound back pack didn't seem unusual.
That was thirty years ago, and thanks to digital publishing I can still carry all my sourcebooks, but now they only weigh as much as my iPad Mini. By making an effort to get rid of things I don't really use at the table and by taking advantage of some innovative products I've drastically reduced not only the amount of stuff I haul around to games, but also the amount of work I do preparing to play. this frees me up to actually play and have more fun.
I'm not going to tell you not to buy a hardback copy of your favorite game and cherish it always. I would be a hypocrite in doing so, and there are times, like during character creation, when there really is no substitute for flipping the pages of the actual book. But. For every game carry, a digital copy of your game's rulebooks saves space and weight, and isn't going to get cheeto stains or drink spills. Properly indexed, it can be easier to find a rule in a pdf than in an actual book, and you can highlight things you need to remember safe in the knowledge that the highlighting can be easily undone.
Instead of buying a hardback copy of your favorite game, buy a hardback copy and a digital copy. Some companies include a digital copy when you buy a physical copy (Evil Hat's Bits and Mortar program). Even for those that don't, an extra couple of dollars is worth ditching the weight of heavy game books.
How to carry all those PDFs around? There are pros and cons to different digital readers, and blogs that discuss their technical specs and pricing. I'll get to a post looking at a few devices from a gaming standpoint, but for now I'll short cut to say, I had a kindle, I now have an iPad Mini and I like it and use it more.
The 3 x 5 index card is probably the most versatile tool in my GM's Toolbox. I carry a stack around as an idea capture system, and have it set up to organize those ideas as they come in. Look up the Hipster PDA. My gaming stack is organized into categories like People, Places, Things, Events and Rules. Embrace the Minimal GM idea that if it doesn't fit on one index card, the idea is too complex and needs to be broken down.