For general Makar Sankranti related information, the Wikipedia link (as usual!) provides good information -- http://en.wikipedia.org/wiki/Sankranthi

For Pune specifically, I can think of the following (I am not saying these are completely Pune specific..):

1 The 'Til Gul' Sweet Delicacy - As the name suggests, made from Til and Gul are distributed by people amongst each other. The Marathi expression - 'Til Gul Ghya, God Bola!' is also commonly used when distributing 'Til Gul' (Quite literally, translates to - 'Have Tilgul..speak nicely/sweetly/ !')

Another sweet item made during Sankranti is 'Halwa' - made from sugar.

2 Wearing black (especially amongst women).

3 Kite flying - this has always been at a much lower intensity than that seen in Gujrat and Rajasthan. And seems like its dying down even more :(

4 'Haldi-Kunku' ceremonies...