I've been whipping out quick-and-dirty USB-to-3.3 V supplies for XBee experiments. All it powers is the XBee (ser 1) and a couple of low intensity LEDs on the DIO lines, with a maximum total drawn current of 50 mA. A simple 2950 LDO, a 1N4148 diode for sanity, and a couple of tantalum capacitors. In most cases I can squeeze everything onto the back of the breakout/mounting PCB of the XBees.
Would this simplistic solution be OK for the simplistic 3.3 V requirement?
(Note: the regulator is a 2950 LDO, not 7833 as Fritzing insists on inserting into the schematic.) Additionally, I also have a 22 pF ceramic capacitor off the VCC of the XBee to ground (but it's not a part of this power circuit).