1. Using cash only is a way of controling how much you spend, if you want to go out to lunch and only have $6, you know you can't afford to go to a sit down restaurant. You can't spend what you don't have.
It does NOT work for the purpose you described, tracking your expenses. Using cards would be much better in this case as you get a monthly statement that list all your purchases. The problem is the statement just tells you where you spent your money, not what you spent it on.
2. A spreadsheet is a great tool for understanding your expenses. With any type of program you use, a spreadsheet, quicken, or pen and paper, unless you write it down on a regular basis, it's not going to work.
Getting a notebook that you keep with you while out shopping, running errands and writing down all your purchases is a great way to start.
However, my suggestion for you is to get a envelope that you keep in your purse or your car. Every time you make a purchase, get a receipt and put it in the envelope. Now you have a record of your purchase with out having the time to write it all down. Once a week take out all the receipts and sort through them. At this point, you can enter the information into a computer program for better control, or just by looking at them you can say "wow, I stopped for coffee 6 times this week, I don't remember that".
3. Coupons - a lot of work for little reward. Years ago I used to purchase the Sunday paper for the purpose of getting coupons. The paper cost $1, but it was rare that I didn't use at least $3 in coupons, usually $5 or more. However, I now find that I rarely use $1 in coupons from the paper. The problem is most of them are save a $1 off 3, I don't want to have to buy 3, or they expire too quickly. I do use coupons that I easily come accross, like the BJ's ones mailed to us monthly, but I don't put a lot effort into it. I find easier ways to save money.
Just by taking a few small simple steps, you can start to manage your finances. Just find what works for you. Here are some things you may want to try.
1. limit eating out or take out to once a week
2. get a refillable water bottle, insulated cup to take your favorite beverage along with you when you leave the house avoiding those convenience store stops or a quick drive thru.
3. make a grocery list each week, buy only what's on the list
4 always review your receipt immediately after making your purchase, In the past few years things have improved greatly, but I still find many items are priced incorrectly, charged sales tax incorrectly, coupons not scanned correctly, etc.
5. plan out a week's worth of meals so you're not buying extra
6. never pay full price for anything (okay, maybe never is extreme), look for clearance items, sales items, or coupons
7. ask yourself "do I really need this"? By nature most people are impulse shoppers, you see something and say to yourself "that's interesting, I could really use that, my friend has one, etc. Just take a second to ask yourself to I really need it before tossing it into the cart.
Good luck.