Without knowing what model MacBook you have, it'd be hard for me to say exactly how to fix it, since the trackpads are different for different models. However, I can suggest a software workaround: Use tap-to-click. Start by going to your System Preferences, click "Keyboard and Mouse", then go to the "Trackpad" tab. Under "Trackpad Gestures", click the "Clicking" box. This doesn't actually fix your depressed-trackpad hardware problem, but will make it so you can just tap the trackpad to click something instead of having to push it down.
In general, magnetic screw mats really help with keeping screws organized. If you're looking for an iPhone-specific solution, you might like the magnetic screw mats that iFixit sells for the CDMA (Verizon/Sprint) iPhone 4, the GSM (ATT) iPhone 4, the iPhone 3G/3GS, and the iPhone 4S. For a more general solution, there's this magnetic organizer mat. It even has little trays for non-magnetic parts :) Edit: I've used magnetic mats in my repairs, and have never had a problem with them. To be on the safe side, just keep the LCD and battery off of the mats, and you should be fine. The magnetic field from these type of mats isn't strong enough to damage things from a distance. :)
Well, you're (mostly) in luck! This guide on iFixit has a step-by-step, location-based guide to what size the screws are, and where they go. 1) Other than the pentalobe screws for the bottom dock connector (which you can get here and replace with the iPhone liberation kit), it looks like the rest of the screws in the iPhone 4s are standard Phillips screws. If you still have all your screws, though(and it sounds like you do, even if they're not all in your phone), you can compare them against the guide and see which goes where. If you are dead set on getting a new set, it looks like you can get them from amazon here or here, though I've never used those supplier and can't speak to how good the screws are. 2) The guide I linked to above will show you what screws go where. But, if you're looking for a RIDICULOUSLY useful all-in-one solution, I personally recommend this: it's a magnetic screw mat shows you where your screws should go on your iPhone 4s, and will hold your screws in place while you reassemble...
I had this problem with my phone, and it ended up being a problem with the USB cable. Getting a new cable fixed everything. Have you tried to connect your phone to your computer with a different USB cable?