I'm trying to give up, or at least drastically cut down, on the soda. It's not going well.
Is it a carbonation thing, or you really like the flavor of whatever soda?
If it's primarily carbonation (I feel ya there), you can always create your own mixes with a seltzer, which is what I do, and carry them along in whatever reusable drink container you prefer (Nalgene is great for BPA free, and you can drop ice cubes in it since the opening is so large). I like to combine a strong flavored juice, like cranberry, with a seltzer; since the flavor is already strong, it's not reduced too drastically by the water, and you can make it weaker or stronger as you prefer -- I like a strong, throat-searing bite to my carbonation.
You can also do the SodaStream thing, but only do that because you like the idea and flavors available, not in some vain attempt to save money (you won't), or the environment (you won't).
But, if it's the caffeine, I'd suggest weening yourself off very slowly, or you will be a miserable human during withdrawal.