Instead of giving away hundreds of small things that people will forget give away one thing that leaves an impression.
And a huge LEGO set is a great candidate for that one big thing. There is a big overlap between devs and folks who love LEGOs. They are both builders after in their hearts.
Now, some important considerations:
You need to commit to it too.
Don't do 3 different things like that at a conference. Focus on one play like this at a time and try other cool ideas at another conference.
Folks from Sigma Computing ticked all these boxes. Love it!