EXTRA HEADPHONES for the Nano - trust me he'll lose them. I think we've been thru 10 pairs.

Try TJ Maxx, Marshall's, Staples. I've gotten Skull candy at all three of these places for less than $10. I've also gotten Phillips for less than $10 at CVS and Target.
Hexbugs are cheap - the nanos are around $7 and the bigger ones $10. They are fun. The kids turn them on and let them loose. You don't need the terrarium or whatever it is they call it to use them.
There are some Nerf Guns that can be had for around $10.
A Baseball hat from his favorite team. I got a Boston Red Sox hat on sale at JCPenny for $5.77 on Sunday - Well, actually I got 2 for $1.54 after my $10 off $10 coupon

but the sale price marked down for $29 was $5.77.
This one may seem a little crazy but my kids like to get Christmas tree ornaments.
Target has Cuponk, Connect 4 and Trouble on sale for $9 this week. Tranformers are $8.49 and Uno and Hotwheels for $4.
A little more than $10 but a Lava Lamp - $14 at Target - my kids are fascinated by them.
Lowe's had some build it yourself craft kits for under $10. Cute things like banks, games, toolboxes, birdhouses. Very very simple to make. We made the banks and games with just a hammer at our Cub Scout meeting in under a half an hour. To go along with it they have the Lil helper tool set for $15. It comes with real working hammer, pliers, screw driver, etc. Home Depot and Sears have similar sets. DB got this for my middle DS when he was 8 and with the reminder that they were real and not for banging on furniture, etc. but for working he has gotten a ton of use out of them and he keeps and uses them carefully. In fact he has asked for a new toolbox for them for Christmas.
Bandanas and other crazy stuff for playing pirates, motorcycle gang, cops and robbers, army etc. My 8 &10 yo love to do this.
Good Luck