An elevator speech is a short pitch meant to introduce the important aspects of a topic or concept in 30-60 seconds.
It is helpful to think in terms of an elevator speech when preparing for a poster session at a conference, because it can help you to ensure you convey the most important parts of your research in a quick, engaging way. It can also help you feel prepared if you are nervous to talk to people during your session.
A handout is a great way to send listeners home with a reminder of your work and your contact information.
Conferences and other events can be hectic and attendees will likely be overwhelmed with information. A handout is a good way to remind them of your work and offer ways to get in touch with you if they so choose. This can be a simple 8.5x11" sheet or half sheet reiterating your key points and contact information.
Some of these resources are for lightning talks, which are a bit longer than elevator pitches, but will offer some helpful considerations and ideas for how to prepare for your poster session.