I'd take the goat across first. The lion left behind wouldn't eat the yam.
Then I'd take the yam across, but bring the goat back with me, leaving the lion on one side and the yam on the other with the goat in transit.
Then I'd take the lion across. This time, the lion and yam would both be on the far side and still wouldn't eat each other.
Finally, I'd bring the goat back across and hope the lion wasn't so hungry after all the delays that it would eat me.