I have some I2C sensors which are capable of running from low supply voltages. Host microcontroller has 3,3 or 5V supply, which is usually out of absolute maximum range, when I2C device is supplied with e.g. 1,8V. The sensor is usually very low power, which means simple emitter follower could do the low voltage supply.
The circuit schematic is shown in following drawing (click to enlarge):