Use a re-usable paper cup (that would mean loss of bamboo trees)?
Use a steel tumbler but wash it with water that will be recycled (that would still reduce the already depleted fresh water) ?
To save electricity:
Remind people to switch off lights by pasting print outs on backs of doors (that would mean loss of bamboo trees)?
Allow the light to be wasted and save trees (that would mean loss of electricity)?