Always keep a buffer of 6 months salary. Tackling the individual ones however:
1. Mobile Phone Plans
Circles Life is hands-down my favourite telco provider to date. Not just for the price, but they also hold cool hangouts for their Circles Life users! For eg. I recently went Light Saber sparring at The Saber Authority, kindly organized by the Inner Circles team. Amazing outing for a Sunday evening, and perfect for Star Wars fans.
Use my referral code JUNUS during your Circles Life signup and get $34 off your registration fee and also UNLIMITED Data free for 3 months.
2. Birthday Celebrations
I am assuming that it's the birthdays of people whom you don't really know (because you would already know the birthdays of the people you really care for). If you are being 'coerced' to 'contribute' to someone's birthday present, and feel that it's getting too expensive, be firm about setting a limit.
3. Wedding angpows
Unless these are close friends whom I genuinely care for, I usually am not a fan of being asked to a wedding just to fill the table. However, if you really have to go, I am afraid you would just need to pay for it.
4. Last Minute Trips
This is what your emergency buffer is for.
5. Ad- Hoc Medical Examinations
Likely to be the most costly if it's extensive. See if your insurance covers it - if not, you would also need to tap into your emergency funds.