The binary code 0011101000101001 that Brainiac 5 wrote on Alex's cast translates to ":)", a common ASCII depiction of a smiley face.
Kara mentions to Brainiac-5 a cat that she found after she arrived on Earth whom she named Streaky. This is a clear reference to Streaky, the supercat owned by Supergirl in the comics. He first appeared in Action Comics #261 (February 1960).
First appearance of the Legion of Superheroes from the year 3000, with Legion flight rings. The rings also allowed them to time travel.
Samantha has only one scene as a civilian; for the rest of the episode, she's dressed in her supervillain costume.
In most portrayals, Brainiac-5 is depicted with green skin and yellow hair. In this version, he has blue skin and white hair.