Well... I got a spare tire for my 135i. I was really just uneasy about driving far from home without a viable spare. My local BMW dealer hooked me up with a deal. I got a alloy 17 inch wheel/tire from an e46 and the jack kit for the 135i. I paid 220 euros for the tire & jack kit. Here are some pics and the part numbers.
Alloy e46 wheel & tire: 36 11 0 445 045 - 120 euros
jack kit 71 10 6 73 536 - 100 euros
The alloy wheel and tire are very light - about 7lbs I would guess WITH the tire! Also the rim is narrow, 3.5 inches I believe. 3.5jx17. The tire is the same height as the normal tires. When I placed them side by side the overall dia/height is the same. Plus the grey alloy wheel looks way more sexy than a steel wheel from an e60. :P
The jack kit somes with alot of stuff: the Jack & ratchet, wheel chock/wedge, torque wrench, work gloves. And directions on how to change a tire! lol
I also test fitted the mini spare to make sure it clears the 135i's big front brake calipers. It does!! This is really the way to go I think. At first I was thinking of a full size option... but that would really cut down on trunk space. IF I were to get a flat I could always throw on one of my winter tires to get me around. But this mini spare is for an emergency so I don't have to wait on AAA or ADAC to come for hours on end. I think its more for my peace of mind than anything else.