When all you have is a hammer...
As the saying goes, "When all you have is a hammer, everything looks like a nail...". This is never truer than when you decide to do a quick repair and decide you can make do without the proper tools on-hand. My advice for anybody who decides to try this is this: DON'T. Nothing makes a job more frustrating than trying to make a what should be a quick repair without the correct tool on hand.
For example: This past winter my battery died while I was at work. No snow on the ground and I am parked on a hill so I roll-start the car and drive to the nearest auto/hardware store. MISTAKE NUMBER 1: instead of buying a battery and taking it home to install (where the tools are), I figure I can borrow a screwdriver and wrench and do this in the parking lot to save a 20 minute trip back with the old battery. 4 different tool purchases and 45 minutes later, as it gets darker and colder, the old battery is no closer to being removed than it was when I pulled into the parking lot. Frustration being at an all time high, the new battery is used to jump start the car and I proceed home where in a well lit garage with the proper tools it takes all of 5 minutes to complete the job.
Need another example? Being a good son-in-law, I decide while visiting my wife's family to replace their bathroom sink fixture. Again, my tools are 1 hour away so I figure I can make do with what tools are on hand. MISTAKE NUMBER 2: some jobs require the correct tool for the job - any substitute will only result in frustration, damaged work, or injury. After spending close to an hour attempting to remove the old fixture with channel locks, pliers, screwdrivers, and every other tool short of a sledge hammer I made a 20 minute trip to the hardware store and purchased the correct tool, a basin wrench. Once this tool was used, the replacement proceeded quickly with no more cuts, scrapes, bruises, or cursing.
If you are the type of person who likes the occasional do-it-yourself project, then you probably have a decent set of tools already. The well stocked toolbox should have a variety of screwdrivers, wrenches, pliers and other tools for any basic repair. If you have been doing this for more than a few years, you may also have acquired a number of specialty tools as well (i.e., snap ring pliers, locking pliers, torx drivers, basin wrench, spanners...). You may find (as I have) that you tend to collect a new tool or two every time you start a new project. Here are a couple of tips for managing your tool habit:
Buy quality tools - I have purchased my share of cheap tools and they typically end up broken, bent or otherwise useless. If you plan to use it more than once and it is not emergency, invest a little extra and purchase a tool you will have for a while.
Don't have the right tool for the job, borrow it! - What are friends and neighbors for? If you have a job that requires a special tool, and you doubt you will need it again in the next 10 years, ask your neighbors and/or friends if they have one you can borrow. You can save yourself a few dollars on a tool you might not use again and may also benefit from suggestions or advice from somebody who has had to use it before.
Can't borrow it, rent it - you would be surprised at the tools you can rent reasonably. In some cases, you can even borrow the correct tool for the job for free if you are making a purchase from that store (I have taken advantage of this from auto part stores on a number of occasions).
Organize your tools - As you collect tools, you will notice that tools fall into certain categories. My basic toolbox has the everyday tools you would expect: screwdrivers, pliers, wrenches, socket sets... For other tools, I store them by the type of job I use them for so I always know where to find them. Pipe wrenches, basin wrenches, spanners, solder, and other plumbing related tools/supplies are stored in a the plumbing crate. Painting supplies like rollers, brushes, and edger's are stored in the painting crate. I also have a crate for electrical and hobby supplies. By keeping my tools organized, I keep my toolbox to a size I can manage (and carry) and always know where to look for the tool I need.
Don't be afraid to have more than 1 - some tools are useful in many places and inexpensive enough that you might want to keep a few on hand. Screwdrivers, hammers, tape measures, and utility knifes are examples of a tools that can be found in a few different locations around my home. A small toolkit for the car is not a bad idea either (see example above on trying to change battery...). I try to keep at least a one of each type screwdriver, a pair of pliers, and a few other basic tools in the trunk just in case of emergency.
Keep some basic hardware on hand as well - Many people have all the tools they need, but sometimes cannot find a simple nail or screw to hang up a picture. It pays to keep some basic hardware "in stock" since you never know when you will need it. I have a simple organizer hanging on the wall of my garage with a small supply of the most common types and sizes of nails and screws I commonly use. These range from finishing nails to decking screws.
One final reminder - While it may seem that I am making light of trying to do a job without the proper tools it can be serious problem. Using a tool to do something it was not designed to is one of the easiest ways I know of to damage the project or injure yourself. Using the right tool for the job will reduce your frustration as well as help you complete the job without damaging yourself of your project.