Depending on the model 1500 watt inverter should be fine.
I haven't used a Keurig style on the road, just a regular small 5 cup type which ran about 800-900 watts.
Keurig Desk Pro (makes 8 ounce cups only; draws 700 watts) Keurig Mini Plus K10 (makes 6, 8 or 10 ounce cups; 1425 watts) Brew & Save Refillable K Cup.
I have a 3,500 watt invertor and the Keurig 45 , it does just fine.
I would guess a minimum would be 2,500 Watt to be on the safe side. There is always a bit of voltage drop using an invertor.