Thanks all for your comments. Variacs tend to be big and heavy, and are usually designed for higher power than I need. Adding an extra step down transformer for voltage limiting / isolation adds to the weight, and does not provide any current limiting, stability with respect to input voltage fluctuations, etc.
I was really looking for a small, portable, self-contained benchtop unit, rather like the Peaktech unit mentioned above - but with somewhat lower power - and cost. Anyway, that's a good starting point. Further suggestions along such lines are appreciated.