Addition to a voltage indicator, would be a plug in receptacle tester,(that shows proper Neutral and Ground), with the button on top for circuit breaker testing.
Small inexpensive Sperry Multi-meter with probe ends. Especially if it's an older house. If your old receptacle is only giving you 96VAC, when it should be 110 he'll know.Modern electronics can overheat if voltage is low.
Surge Protectors.
Wonder-bar, shovel, new BBQ Grill, Have him get the house inspected if used, copy of full report. etc,....
New smoke detectors, +1 on fire extinguishers.
Needle nose pliers.
House warming party!!!!! and the beer, tools needed for that too.