A handgun, semi-automatic or revolver.  Any caliber will do.

A holster, one that covers the trigger.  Take a look at the one shown above.

Fifty to sixty rounds of inexpensive, target grade ammunition, not armour piercing or metal other than lead and copper.

Hearing and Eye protection.

Extra magazines or speed loaders, enough to hold 25 rounds or so.

Trousers or shorts with knee pads; trousers or shorts should have belt loops.

A belt, approx 1-1/2 to 2 inches in width, capable of passing through the loops of your trousers or shorts.

Possibly suspenders if your gun and ammunition on your belt are heavy.  I hate it when my pants fall down; although it provides comic relief, it's a trip hazard when moving quickly.

Drinking Water

Sun Tan Lotion

In summer, substantial light colored clothing or

In winter, windbreaker or coat giving freedom of motion.

Sturdy non-skid shoes or boots; I like hiking boots or tennies with ankle support.

Portable chair

Lunch

A Friend

Sense of Humor

Good luck charms to improve accuracy (I use a Swiss Army knife for which I've never lost the toothpick)

A bag to haul home your trophies