Activate the following cheats by entering the corresponding codes at the Mos Eisley cantina:
CHEAT FUNCTION - CHEAT CHODE 10 extra Studs - 4PR28U 500,000 extra Studs - HGIGHF All characters - UDLRAB All weapons in Character Editor - BIGGUN All clothing in Character Editor - 867539 All bonuses - ABACAB Obi Wan's ghost - BEN917
To easily gain Studs, select the "Escape From Echo Base" level. Choose any blaster character and Gonk droid. At the part where you see a square of silver Studs, with the first grapple hook press A. Build the computer thing and go through to the next room. Change to the Gonk droid when you start sliding down the hill and go back into the room you just came from. You will find 14,000 Studs. Repeat as desired.
The self destruct isn't a completely useless extra. Though blowing up your droid may seem like a bad idea, it is worth noting you don't lose studs (from the act of self-destruct), meaning that you could blow up to prevent losing studs from falling or you can send your droid, which is usually ignored by enemies, into the middle of a bunch of them, and boom. If you opt for the invulnerability extra, it's pretty pointless entirely, but it's an option open to other players.
Double score zones lets you earn double the credits from studs. Due to this effect, you can exploit it by killing your partner (2 active players only) and taking his money (and vice versa). While you lose a set amount of money, you also earn double that amount because of the double scoring effect.