pcv and grommet, spark plugs and wires, clean MAF, clean Throttle body, all fluids (brake/power steering/front and rear diff/transfer case/transmission), timing belt/WP/idler/tensioner/seals, seafoam/bg44k in fuel tank, thermostat, radiator+hoses, transmission filter, etc
LBJ's if they haven't been done, you need to check the Toyota Owners site if the LBJ's were done by dealer or not... with a 2002, they are covered under recall
brakes - front and rear
get battery and alternator tested from auto part store
inspect the underside for leaks (rear pinion seals and rear axle seals can both be leaking, among other things), inspect valve cover gaskets for leaks
air filter
pull obdii engine codes if you have any
there is a huge maintenance list (more than what I stated above if you are really OCD, just look at some build threads here), it will take you a lot of time and money, but you've landed in the right place
take it one step or item at a time, Rome wasn't built in a day
prioritize the LBJ's and you will thank us later - register at the owners site with your VIN, see if they've been done or not, if not, do that before ANYTHING else besides a fresh oil change and filter if you're behind on that.
a well-maintained 3rd gen 4runner will last 500k miles or damn near it barring no major incidents that may afflict you depending on your luck, some people on the board are unlucky (or maintain like shit) and have the pink milkshake at 100k miles or a bad head gasket at 150k miles, etc which are low mileages for 3rd gen t4r's.