I think that being organized has a lot to do with not being afraid to throw things out. More people than you imagine still have the warranties and instruction manuals for tvs or blenders or vacuum cleaners that they got rid of years ago.
I keep warranty and purchase info (receipts, clearly labeled with date and price of purchase) in an accordion style folder. I try to keep them separated by category: kitchen small appliances (coffee makers, toasters...), large appliances (washer, fridge...), tools (power tools, lawn mowers...), computers and peripherals (external hard drives, monitors, keyboards, laptops...). Then, it's important when throwing out that coffee maker that died to go get the receipt from 1999 and throw it out, too.
I don't keep instruction manuals for the most part, as most manuals are now online. It's easy to find them. So many manuals devote multiple pages to common sense (don't use this toaster in the bathtub! don't use this weed whacker in a swimming pool!), and many of the pages are devoted to technical stuff, like how to replace the condenser in a fridge. Unless you are comfortable taking an appliance apart and repairing a motor, throw out the bulky manual and assume that the repair person that you hire when your fridge stops making ice will know how to fix it without reading your manual.
It is tempting to keep every cord and plug, but, try to keep track of how long it's been since you actually used that plug. Test the plug or cord and see if it goes to anything you currently use. If it doesn't, toss it. Many chargers are obsolete pretty quickly, and extension cords shouldn't be used if they're really old. If you use extension cords for indoor and outdoor holiday decorations, keep those cords with the decorations.
Packaging is one thing I keep, such as the box to a tv or computer, but that's because we move a lot. If you're settled in your house, and don't move around due to military service or a job, toss the box. Places like Home Depot or U-Haul sell tv boxes and specialty packing boxes. If the box goes to a computer or tv that will accompany a child to college or his/her own apartment soon (like if they're 17, not 6), then probably it's a good idea to save that box too.
Be brave and toss stuff out!