Era 3 Preparation

Level up your Laboratory. Level 17 is needed to get Era 3 Coupling by the end of Era 3 without a plus account. Level 12 is needed with a plus account.
Be sure to save enough money (2,750,000) to upgrade your Engine shed right after we hit Era 3.
Get Coupling. If you won't have Coupling by Era 3 but you can get it less than a day into Era 3, you should finish the research for it. 1 to 2 days is more questionable but I wouldn't blame you for getting Coupling. More than 2 days, IMO forget about Coupling and save your research points for Era 3.
Have at least 3-4 free tracks to begin Era 3. Or connect to all Era 3 RGs by using a Map Of Goods. You can't haul a new RG if you aren't connected to it.