The words "Pry" and *perhaps* the slogan "get to the code", but the slogan is not necessary, only add it if you think it improves the design.
Also the "crowbar" in the current logo is kinda cool, working that in somehow would be appreciated, but again, use your own artistic discretion.
Do not have to stick too closely to the official logo, so long as it's in some way reminiscent of it, or at least relates back to the "Pry" project itself (see the website here: http://pryrepl.org). Our previous t-shirt design stuck too closely to the official logo and was worse for that, in my opinion.
I enclose the old t-shirt design in the 'attachments' below, again, we did not like it particularly much, so feel free to do something quite different.
Also remember this is a t-shirt design, so we're likely limited in the number of colors that can be used. In the past we've used "silk screen" printing which has limited the number of colors available to about 3-5.