In 3rd (Codex: Armageddon) Tankbusta models were wearing grenades and melta-bombs in addition to RL. I use the bits from the current Boyz box, and also the Grenade backpacks from the Nobz sprues. The Lootas box comes with one RL. You get enough bits for a ten-men mob with each of these three boxes.
w.i.p. Bustaz
For vehicle RL I use the Killa Kan and Deff Dredd rockit launcha bits. Also Mantic sold RL with their Raptor kit which are sold for cheap on ebay quite often. I replaced some of them with big shootas so I ended with spares for the battlewagons.
The Ork flyer kit comes with many spare missiles as well (in a similiar style to those in the 'Naut kit) - 8 or so - which if glued onto other bits work well on Ork vehicles of all kind.
Also if you convert Deffkoptas with Buzzsaws or Big shootas you can use their rockets for Rockit Launcha conversions.