I would personally recommend saving a percentage from each of your income sources. Doing this will help you develop an "all-around" habit of savings.
That way, if one income source ever dries up (of course we hope it doesn't) you won't simply stop saving because that was the income source you saved from.
Saving a percentage helps you to stay balanced. You can start with as little as 1% from each and build that until you are saving a significant amount on a monthly basis.
To jump-start your savings, take a set dollar amount from each income source. With your example given, you would then take $50 from each income source and then set a certain percentage to save from each every month.
You could save it all in one place, which as you mentioned would give you easy access but that might actually work against you. Because it might tempt you to spend the money when you don't really need to, and then you end up right back where you started with nothing in savings
What might be a good idea would be to save it in 3 separate places. Doing this, you would still have easy access to some of the cash but because a portion of it won't be as easy to access, you might be less tempted to spend it.
It is also cool to watch your money grow in several accounts over time because, although it is the same amount, it feels like more when you spread it out.
I personally probably take this a little to the extreme with multiple savings accounts, investment accounts and even a physical stash of nickels, but like I said, it is really cool to watch each savings pile grow over time.
These are just my personal thoughts but hopefully it has given you a few helpful ideas.