In terms of apparel, it’s better to spend a little more and get specific karting items, also because, for amateur use, except for accidents and sliding on the asphalt, good overalls last a long time. The same goes for the helmet.
Last, but not least, arm yourself with all the necessary kart-care products and tools: rubber gloves, replacement nuts and bolts, a full set of Allen keys (2.5, 3, 4, 5, 6 and 8 mm), a set of fixed or composite wrenches (at least 8, 10, 12, 13, 17, and 19 mm), a couple tubular wrenches, mixed screwdrivers, pliers, pressure gauge, isolating tape, WD40 and all the necessary items to make the fuel blend.