It really depends on the goal of your franchise.
For us, we tend to have various toys and props on display, along with patches and pins that we sell to raise money for our charities.
At a larger convention we had a separate table setup as "Egon's workbench" (with various tools and props on display), as well as ESP testing with a "shock box" (it doesn't actually shock people, it just has a vibration motor which buzzes and plays a sound).
What usually goes over well is if you have photo opportunities available. People loved putting on a Spirit Pack (or foam pack) and posing for photos with our inflatable Stay Puft. It's up to you if you want to charge a donation for this, but we found many people offered a donation to us without being asked first. Sometimes I just hand them a trap to hold up in the photo. If it's a convention and they're cosplaying you can also get great photos with them, especially if it overlaps with Ghostbusters in some way.
Another goal is to boost your social media followers, so have some signage with QR codes to make this easier (and if they pose for a photo ask them to tag your franchise when they post it).
Here's our display at a toy fair we did in October:
And here's our much larger display at a convention:
Most of the time we have to bring everything in 1-2 car loads so we don't (currently) have firehouse walls or a containment unit like some of the bigger franchises. But we have enough that we can bring along to really fill out the space we're given.