I'm sure the synfluid or whatever is good, but any ps fluid from the auto supply will serve you well. I've run plain ol' stuff from the auto supply for hundreds of thousands of miles with great success.
I would suggest that you pick up two extra quarts while there. Replace the filter, then disconnect the return line and put it in a drain pan. Then have someone start the engine and turn the wheel lock to lock while pouring in two quarts of fluid. After that fluid is gone and in the drain pan, turn off the engine. Reconnect the return line and fill the reservoir. Have your assistant turn the wheel lock to lock while pouring in fluid until full.