A pair of genuine Levi’s and a jar of peanut butter.
I was going to suggest you pip down to Anaheim and get him some Mouse Ears but then I saw it’s over 2 hours away. And THEN I saw that you can buy them online for $12!
Gift card to Applebee’s
When I spent a semester in London (not nearly the same, I know), this was a looooong time ago, when we got homesick we found an American food section at Harrods. What did we spend about 10 bucks on each package?
Doritos and Oreos.
So that’s my suggestion!
You may be closer to LA but if you are going to sent a baseball cap, send one from the World Series champs! Or send a cap and goodies from the local team. (You’re from Fresno, right? Send a Grizzlies grab bag.)
A selection of magazines, food, whiskey.
I’m a Peace Corps volunteer myself, and those are awesome ideas. Most of the care packages I get involve chocolate of some sort and little packets of Starbucks Via and Crystal Light (it’s nice to have something to flavor water with). I don’t know how Fijians decorate their homes, but most of my host country neighbors cover their walls with posters and calendars, and everyone loves to share pictures of family with visitors, so maybe a small photo album?
Well, you asked. 
A small aside for this true story you’ve reminded me of: I once had to call the cops on the Fijian finance minister. I was manning the front desk of the Hale Manoa residence hall at the East West Center, a federal research facility located at the U of Hawaii. Residents started calling down around 3am about a noisy, drunken party in one of the common rooms upstairs. It turned out to be a party of Pacific Islanders. The guest of honor was the Fijian finance minister, who was there for a few days for some event. They were having a roaring good time and for the most part ignored my pleas to keep it down. Continued angry resident complaints meant I had no choice but to call the campus cops. They broke the party up for the most part … except for the finance minister, who acted like we were all ghosts whom he could not see or hear. Just continued plunking away on his guitar and belting out selected favorite hits. The cops finally managed to get him secured in his guest room. It was after 4am by this time. The Fijian resident who was hosting the party, a normally pleasant fellow named John, I guess due to a loss of face was angrily telling me which East West Center officials he was going to talk to and how he was going to have my job. I tactfully declined to tell him that it was my last night anyway, because I had just graduated and was poised to return to Thailand, heh.
Anyway, on a more serious note many of the suggestions in this thread are good, but I would avoid sending chocolate, as from personal experience I know how that can arrive as a big, melted, gooey mess when being sent to warmer climates.
Easy Cheese. In my own personal experience there is no consumer good more bewildering to people from other countries. Don’t forget to throw in a box of Triscuits.
Several years ago we visited someone in Ireland and we wanted to bring something characteristically American. We brought containers of Maple Syrup. Most places don’t serve real maple syrup. If they serve anything like it, it’s sugar syrup with added maple flavoring. Real maple syrup was a rarity over there.
Try other American delicacies. Real Buffalo Wing sauce. The makings for Boston Baked Beans. Maple Sugar. Cheez Whiz for real Philadelphia Cheese Steaks (along with Amoroso rolls). Spiedie Sauce. U-Bet chocolate syrup.
Poptarts, rootbeer candy, those little flag toothpicks, canned pumpkin - at least these are the things I cannot get here and therefore look uniquely American to me (an expat American overseas.)
So many American things and brands are ubiquitous all over the world now, it’s weird. Used to be Butterfingers and Reeses and Karo Syrup and corn meal were things I wanted, now they are everywhere.
A touristy coffee table book containing excellent pictures of your home area. Shirt/hat from your favorite team. Artistic wall maps or posters. exotic (to him) foods and flavorings (maple syrup/candy is an excellent idea, also dried blueberries and nuts.
Depending upon the level of poverty, a gift of needles, thread and cloth to his Mother/sisters might also be appreciated.