Class skill: scout
Luckily, KOTOR comes before the time in the Star Wars universe when a Scomp Link interface like the one R2-D2 possesses was necessary to hack into computer systems. As such, your human character will be able to droidishly override the default programming of computers you encounter along your adventure, provided you have the skill necessary to use the computer "spikes" which act as disposable hacking tools. Each task that can be accomplished with a given computer requires a certain number of spikes, but the computer use skill reduces the number of spikes necessary for a job by one for every four points of proficiency you possess in the skill. Unfortunately, this makes computer use a rather point-hungry skill to upgrade, since you won't necessarily see any benefit from adding less than four skill points, so this is a skill you may want to consider going all-in on, and pumping as high as possible, or simply avoiding it and hoping you have a hacker NPC teammate along when you really need one.
Truthfully speaking, computer use can be disregarded as a serious choice for your skill points, at least for your PC. While there are some occasions where the ability to reprogram all of the droids in an area to fight alongside of your party is useful, the designers have carefully made sure that computer use is never a required skill for passing through an area; thus, there's never any situation where the ability to hack a computer is absolutely required, or will accomplish anything that can't be achieved with the use of brute force, or the security skill. If you have extra skill points hanging around, computer use might be useful as a last resort, but even the weakest characters will rarely find it necessary to resort to hacking to get through an area.
Class skill: soldier, scoundrel
Every so often, you'll encounter traps in KOTOR. Sometimes you won't see them coming, in which case a high demolitions rank won't be very helpful, but if you do manage to spot a mine in your path (using the awareness skill), you'll need to have some measure of demolitions proficiency in order to disarm it. You can set a mine that you have bought or found by making a check against the DC of the mine, which is either DC 15, DC 20, or DC 25, with the higher difficulties being, of course, the most powerful mines (which are usually used to guard the most valuable locations and items). When you wish to disarm a mine, you add five points to the DC of the task; if you want to both disarm the mine and recover it so that you can use it later, you'll need to add 10 to the DC. Luckily, mine disabling falls under the "take 20" rule: if you have a theoretically unlimited amount of time to perform an action, you'll be able to assume that your roll on the DC check is always a 20, the best possible result. This means that, when you attempt to disarm or recover a mine when your party is not in combat, you'll stand a pretty good chance at doing it. Unfortunately, the high DC of the more difficult mines still makes demolitions another skill that's unwieldy for dabblers; if you don't have a high enough Intelligence modifier to give you a reasonable chance of succeeding on a DC of 25 or more, you may wish to leave the bomb squad heroics to your teammates. They won't mind a bit.
Using mines in an offensive capacity is rarely useful, though when it does work, you can sometimes find the skill single-handedly killing off an opponent that three party members combined can't defeat. (This can come in fairly handy towards the *cough* end of the game.) You don't find quite enough mines to make this a consistently viable approach to combat, though, and while your teammates cannot accidentally trigger your own mines, they do seem to take a peculiar kind of glee in running towards your opponents and attacking them before the enemies walk over your mine field. In order to properly use mines, then, you'll need to: be able to spot your enemies from a distance away (or have died and reloaded, and thus know where they are or which door they're behind); go into solo mode and plant the mines with your other party members far enough away so that they don't spot the enemy and go hostile; get one of the enemies to spot you; then run back across the mines and wait for your foes to blow themselves up. In short, it's often a little more work than it's worth, but it when it does work, it can sometimes single-handedly win a difficult battle for you.
You cannot use the demolitions skill unless you've achieved a skill rank of at least one.