Of course, if you are in Dotonbori, watch out for the best deals at the 99 Yen shops as they sell very cheap chocolates and other items made in Japan.
However, I think if you want a one-stop shop where you can find a fixed price store for cameras/DSLR, laptops, Casio G-shocks, all those KitKat flavors that seem unthinkable at first, t-shirt, shoes, signature bags, everything under the sun, then Don Quijote is the place to go.
So exactly where is Don Quijote? A simple googlemaps search will show you that Don Quijote is a famous discount chain in Japan (and in Hawaii I think). If you are in Tokyo, they are all over but I recall shopping in the Don Quijote in Roppongi Hills and the other one in Asakusa. If you are in Osaka and in Namba area, there is one nearby and it is very near that Glico Man (now woman). Best of all, Don Quijote is open 24 hours so any time of the day (or night), you can go there and buy cheap items.
Here is the picture of Don Quijote in Dotonburi. It is the one which has a yellow and red roller-coaster like design and it is the tallest structure if you are standing at the bridge where the Glico Man is. If you can see the H & M store, just turn left there and walk by the river and you wont miss it. .
If you are looking for souvenirs, you can buy it in Don Quijote but the stocks may be limited but if you intend to buy food items, then this is the place to be.
Now, if you are into outlet stores, then head to Rinku-Town. This is the first stop if you are coming from Kansai Airport and you are taking either the Rapit, Nankai or the JR Rapid Train to Osaka Loop line. If you are taking the Haruka Express, Rinku Town is the first station that the Haruka will skip as soon as it passes by the metal bridge that connects Kansai Airport and downtown Osaka.
The above is the very familiar ferris wheel that you can see once you land at Kansai Airport. Yes, that is where Rinku Town is. Here, you can see so many outlet shops. Don't forget to check out the other outlet shops across this area. I recall seeing a GAP and ABC outlets.
If you want to buy last minute items, there is a Seria 99 yen shop here in Rinku Town. There is also a very good supermarket with lots of Nissins Seafood Cup Noodle (Made in Japan) here. In case you are wondering if it is perfectly alright to hoard Nissin Seafood Cup noodles, you will be surprised to see so many Pinoys checking in like 3 to 4 boxes of these cup noodles. The reason is that the taste and the quality of the noodles is very different from the Philippine version. Anyway, the name of the store is in Japanese but the shop shares space with Seria. Below is the picture:
The grocery that I am referring to is the Japanese characters between Compass and Seria. They also have cheap Meiji Almonds there and way cheaper than those in Dotombori (roughly 79 Yen per box). As you can see, these shops are just at the food of the ferris wheel.
What I did was I left my bags at Kansai Airport locker and went back to the Kansai Airport Train Station to go to Rinku-Town for last-minute shopping. I was able to buy quite a lot so to those planning to go and shop at Osaka, think of these recommendations =)