If you plan to order larger than personal amounts, which could get you a controlled delivery, then you don't want evidence on your computer of your SR activities. At a minimum you should put Tor Browser Bundle and your PGP program on a Truecrypt encrypted thumb drive. GPG4USB is a great portable PGP program that you can run from a thumb drive (or anywhere, really). Check the link in my signature for a tutorial on how to use it. Your ISP doesn't know what you're browsing over Tor, but they can tell that you are using Tor. This isn't a problem generally, because millions of people use Tor for many reasons, so simply using Tor isn't evidence of a specific crime. However, if you want to hide your Tor use from your ISP anyway, you can use bridges. Look through the Security forum to find out how to do that. You can also use a VPN in combination with Tor, or even a VPN + bridges.