Prepared meal shops

When I last travelled in Japan , about 3 years ago, one of the hotels I stayed at was near a store that sold ready to eat foods. You filled up a container of what ever foods you liked, such as tempura, crispy chicken or salads and paid buy weight for what you took.
I found it very useful after a long day of sight-seeing and also value for money as I was on a budget.
My questions are; what is this type of store called and how do I find more stores like this when I come back to Tokyo next month?
Thanks in advance.

Do you happen to remember exactly where that was?
There are many different types of these... did you fill it into plastic "bento" takeaway container, and did it come with rice so that it makes a whole meal, or did you just pick up whatever bits, or did you fill bowls and trays, and you ate in at the place?

If it was complete takeaway, I would call it "o-souzai-ya" (just one example here),
http://souzai-en.com/

...and if it had some "eat in" area, we tend to call it "deli," such as this place:
http://www.e-organichouse.com/deli.html

There are "teishoku-ya," where you can eat set meals, or select rice, soup, main dish, and side dishes, etc.

You can ask for "sou-zai-ya" which means delicatessen.

But the only place I can really think of that allows you to use tongs to pick up food by yourself, as opposed to asking the clerk to do that for you, is the Origin franchise.
http://pkg.navitime.co.jp/toshu/

If you don't mind calling out for the clerk to pick food that you point through the showcase, you can go to any department store basement to find a variety of those kinds of stores.

AK and I seem to be posting at the very same minute lately :)

It's called "Hakari-uri"(weight and pay). You can be seen at butcher and department stores food courts mostly these days.