Domestic microwave ovens, even small ones, suck back a lot of power. Typically, they consume between 700 and 1000 watts and are usually 120V AC appliances since they're meant for home use. You can use a 12V DC to 120V AC inverter, but a 1000 watt inverter will cost about $Cdn 500(~$U.S. 325).
A quick Google search turned up some sources for lower powered 12V DC microwave ovens in England that run about 350 pounds (~$U.S. 455). That's still not cheap, and they need to be hard wired since they draw 65 amps!
There are more options available in terms of refrigerators. The cheapest solution is a thermoelectric cooler manufactured by Coleman, Igloo, or Koolatron that runs off 12V DC. They come in many different sizes and cool to about 40° below ambient air temperature. By reversing polarity, they can also be used to heat food. In my experience, they don't cool well if the ambient temperature is much above 70°F, so if you are running without AC on a hot day, things might be a bit yucky after a long drive. A better, but more expensive solution, is to get a portable refrigerator/freezer that uses a conventional compressor to cool. These are available from Dometic, Koolatron, and a handful of others for around $U.S. 800.
<font face="Verdana, Arial" size="2">Originally posted by shahv2000:
Is there any portable microwave oven or refrigerator which can be used on the odyssey?</font>