- Your airport tax is paying for the transit area amenities, so go ahead and check-in early to use them.
- Transit areas of all terminals are linked by the internal Skytrain. Visit the butterfly garden in T3 for free, places like that usually charge $$.
- There is also a cactus garden, sunflower garden, etc.
- Payphones near the gates are free for dialling local numbers. Use them to inform people that you are departing or arriving.
[Edit 06 Oct 2015: look for this sign for the free calls]
- Fish feedings are held at fixed times every day. If you are there at the right time, ask the staff to give you some fish food. The koi at T3 will eat from your hand. [Edit 01 Apr 2015: Feedings are held at T2 also but the fish are skittish and won’t approach closely. Timings are ~9am and ~3pm daily.]
- Some of the seating areas have charging points. No more awkwardly crouching by a pillar to charge your phone.
Downside: Changi is really stingy with the free wi-fi. Only available in transit area, plus need to key in phone number to get an activation code. Compare this with other airports, where wi-fi is available in arrival/departure areas, and you just have to connect and click on a button on the redirection webpage.