Car questions.

As others have mentioned, parts that are good to pull for extra $$ are catalytic converters, radiators, starters, alternators, the battery, and any aluminum rims. There is usually a lot more you can pull off, it all depends on how much time you can/want to spend on each car. There are usually aluminum engine parts like cyl heads, intake manifolds, mounting brackets for the alternator, etc. If a car is a 4 cylinder econo-box, there is a better chance of items like cyl heads and intakes being aluminum compared to an older big heavy v8 vehicle. Something I do as well is when I'm prepping a car for hauling, I grab any loose steel from inside the car such as the tire jack/handle, and loose steel inside, any spare parts from an interrupted/given-up-on repair, loose brake drums/rotors, etc. This is because if I separate that material out, I'll get #1 prepared steel for it, which is worth about $80 more per ton than car bodies where I am. For myself, it's worth the extra handling of piling it up till I have a batch, and then hauling it in.

As for fluids being drained, you'll have to check with the yard you're going to be hauling to. Where I am, the engine and transmission oils need to be drained, and the freon out of the AC. For removing freon, you can either buy some kind of unit that drains/filters/recycles it, but that's a fairly large expense. You might check with shops that do air conditioning; here we have a couple that will drain vehicles of refrigerant for you. If you have 5 or more, they'll send out a truck to do it (at no charge, as they keep the refrigerant as their fee). If it's only 1 or 2 vehicles, you have to drag the vehicle to their shop, and they charge $15.00. Lots of the time, older vehicles being scrapped out or accident vehicles won't have any refrigerant left, which is good as it's a hassle. As well, the gas tank needs to be drained, and then either removed from the vehicle and dropped off separately, or at least have a 8" diameter hole cut into it to ensure there's not more than a few drops of fuel still inside. If you are going to get into scrapping cars in any major kind of way, you'll want to invest in a fuel siphon/filter system of some kind. Not having to buy gas can be a nice bonus. I use the electric pumps from fuel injected vehicles (my personal favourite is the frame-mounted "booster" fuel pump that some late-80's Ford trucks used in addition to the in-tank pumps. They're mounted along the inside of the LH frame rail just behind the front wheel). You can also use the in-tank pumps from most vehicles once you remove them from the fuel tank sending unit and rig up hoses and a filter to them.

Lastly, on catalytic converters. Lots of vehicles have a system that uses multiple converters, so don't forget to check right at the exhaust manifolds for a "pre" converter, as well as the usual spot under the car. Some of them are worth quite a bit, especially the imports.

If the yard you're hauling to does not require the coolant to be drained, then you might want to consider leaving aluminum radiators intact in the vehicle. Up here, for the $0.23 you get for dirty aluminum rads, considering average weight for me was around 6-7 lbs, I would rather lose the $1.50 or $2.00 and not have to clean up and dispose of a few gallons of antifreeze, and go through however much floor-dry to clean up spills.

Also mentioned have been heater cores. If it's a vehicle that the heater core is mounted inside under the dash, it's an awful lot of work for a small brass/copper or alum rad. If it's mounted outside the firewall in a plastic housing, usually a sledgehammer is a quick way to get it out and make a couple bucks. Some cars (especially RWD GMs) also have an AC evaporator core mounted outside the dash in a fairly flimsy plastic housing that you can also whack a couple times with a sledge and have a nice chunk of aluminum rad

Something else you should consider are the mercury switches on a vehicle. They are used on most hood and trunk lights, as well as some ABS systems. Where I am, these need to be removed before you haul a vehicle in. The same yard that buys the cars also buys the switches for $1.00 each. I'm not sure if they buy them for recycling the mercury, or for an environmental program. It's not much money, but it's better than having to remove them anyways, and then having to pay to have them disposed of as hazardous waste. In case you don't know, the mercury switches are the small cylinders that are screwed or mounted on hoods and trunks that when they are opened, the mercury inside the cylinder sloshes around until the right angle of the hood/trunk is reached, and then it covers a pair of contacts in the switch, completing the circuit and turning on the light. As for the ones used in ABS systems, to be honest, I don't have a clue. An awful lot of vehicles made in the last 20 or so years have ABS, yet I don't think I've found more than a few double handfuls of ABS mercury switches after prepping god knows how many vehicles at a wrecking yard. If anyone knows more about them, I'd love to hear it. Even if your yard doesn't require the switches to be removed, you should anyways as mercury is really toxic, and the switches only take a couple seconds to remove.

edit- I forgot to add. If you scrap a lot of cars, keep the keys. They're zinc-coated brass (other than a few older Fords I've seen that used aluminum keys). While it takes a while to fill up a 5-gallon pail, it's nice getting $150 for some scrap that you would have gotten $10 for if you left it in the car