While working on our first Android game, I came across a tool that let's you combine all your small sprites in to a single sprite sheet that will be loaded by your game engine. The tool is called Texture Packer.
The tool will try to fit all the images you throw at it in the smallest possible spritesheet. If you want, it can also crop and rotate the images to make it possible to fit even more images to same space. Several different game engines are supported, so for example AndEngine which we currently use, the tool will create one image file, one XML data file that contains the locations, rotation etc. information of the sprites in the image file and one Java file which has a constant for each of the sprites for typesafe handling of sprite loading.
Packing all your sprites to one image has multiple benefits. OpenGL ES requires the textures dimensions to be a power of two. This way, if you have a single texture buffer for each sprite, you end up reserving lots of extra space for nothing. With single, tightly packed spritesheet you usually can get away with considerably less empty buffer space. Using a single TextureAtlas for multiple textures has performance advantages in both loading the textures as well as drawing them. Details about advantages in drawing performance are explained here.
The tool is easy and intuitive to use. The developer is friendly and fast to response to any problems you might have. And it does now have a version for Ubuntu, which was perfectly timed as I had just moved my development to Ubuntu from Windows as I kept having issues with Windows filesystem and Maven.
As I'm starting to sound like a marketing droid here, I will state here that I don't have contacts to TexturePacker or it's author, I didn't receive any payment from this post. Andreas Löw, author of TexturePacker, was kind enough to provide me with a free Pro license of TexturePacker.