The first costume Kara tries on is a mix of several elements from the various costumes worn by Supergirl over the years. It is similarly revealing to the costume of Power Girl who is Kara from a different Earth. The headband comes from her 1980's look, just prior to her being killed off in the Crisis of Infinite Earths story line. The bare midriff comes from the costume that has been generally used in the comics and animated appearances since the character's revival in 2004. The hot pants come from the costume worn in the 1970's. The costume she eventually settles on is inspired by the most iconic version of her outfit, with touches inspired by the costume worn by Henry Cavill in the DCEU films. The most noticeable change is the lack of yellow backing behind the "S" symbol.
Kara lifts her glasses from her eyes before using her X-Ray vision. In the comics it is often stated that Clark Kent must do the same because his super-vision can melt the lenses.
The double hoop shape of the Kryptonian prison is visually similar to the "double hula hoop" used to restrain the Kryptonian prisoners at the beginning of Superman (1978).
The newscast after the plane rescue refers to the bridge that Kara guided the plane through as "Otto Binder Bridge". Otto Binder was a comic book author, who co-created the character Supergirl in 1959.
In the comics, Hank Henshaw becomes a villain who fights Superman several times, even impersonating him at one point.