So I find myself working for a few weeks in a small team of four, including me. Quite a change from my last job at a 300+ developer shop where I'd been part of the adoption of an agile methodology.
I've been sneakily introducing useful tools like a continuous integration server and am surreptitiously starting test-driven development.
What other agile project management and development practices are appropriate for the smaller shop?
Well, to me, your actual configuration is much more appropriated for Agile than a 300+ developer shop (not really sure how Agile was implemented there, I'd love to hear more about that as scaling to that size requires a very high level of maturity on Agile IMO).
So, my answer would actually be: starting with 4 people, all values and practices are appropriate and valuable. Actually, what Agile methodology did you adopt previously? What practices did you implement? What makes you think they wouldn't be appropriate?
PS: If I may, try to see beyond engineering practices, Agile is not (just) about that (this is especially true for Scrum). Practices such as Test Driven Development, Continuous Integration, etc are nice but they are just a mean, not an end. They won't suffice for a successful Agile implementation. Agile is a business oriented organizational pattern. In other words, technical stuff is not really the best starting point when implementing Scrum, you should start with organizational things.