Notion number two is much more important. Not being able to access the information once it has been brought to the past completely defeats the purpose of the time travel in the first place. Therefore how you approach problem one is dependent on the answer to problem two.
Note: I'm assuming that we're time travelling from the present day, as extrapolation of future technology is too big of a variable. The same principles will apply to if we're travelling from, say, 2500, but the exact time ranges may be different.
0-10 years: If you're travelling back such a short time, you don't really need to worry about it. Most electronic storage systems have backwards compatibility - you could travel back to 2006 with an external hard drive that has a USB 3.0 connector and it would work fine in a laptop's USB 2.0 slot. Many file formats will stay the same over this sort of time range, or at least have compatibility modes (we're still using .mp3 files for music; .doc/.docx and .xls/.xlsx are essentially interchangeable). You may have some issues depending on what type of information you're bringing back, but all in all you'll probably be able to find a way to make it work.
10-25 years: At this point we need to start taking past technology into account. In 1991, USB connections didn't exist, so our external hard drive from earlier won't be much help. You could probably get away with using CD-ROMs, but you'd need to be careful about memory overflow and such problems that would arise by trying to port modern files onto old systems.
25-50 years: At this point we're nearly out of options for electronic storage. We could be going back to 1966, and that's too far for computers. The programs don't exist, the file types may not even exist... Hell, the first "modern" computer was ENIAC, built in 1973. Your best bet would probably be to bring your own laptop along in addition to the hard drives full of information, jury-rig a plug to connect into the electrical lines, and just go that way.
50-100 years: This time jump can put us back before the idea of a computer was widespread. (Yes, Charles Babbage and Ada Lovelace were playing with the idea of computers in the 1800s, but it's not the same ballpark.) However, electricity is widespread enough that you could do as I mentioned above, simply bring your own laptop, connect to power, and pray that nobody asks you what that thing is.
100+ years: At this point, we're out of options. Even in the late 1800s, electricity isn't generated on a wide enough scale for bringing a laptop to be a viable option (unless you bring a solar-rechargeable battery, as @D.Hancock suggested), and going back further than that is even worse. If you're going back further than electricity, you're going to need non-electric storage. And that means books. There's a reason we as a species have been using books for so long, and it's because they're efficient. We can fit a lot of information on a page, they're easy to pack up nicely, and (most importantly) they don't require special technology to use.