S for Something which starts with S

You're missing a few good ones.

A for An

C for Cay

I for In

K for Knight

N as in No (a few of these work with "as in" but not with "for")

O as in Other

P as in Pose

Q for Qing (since Jalapeño is allowed)

T for The

T as in tsunami.

P as in phone.

K as in knife or knee.

G as in gnostic.

X as in xylophone.

D as in djembe.

M as mnemonic.

O as in opossum in certain locales.

Barenaked Ladies - Crazy ABC's

"is that your first or last name"

G as in gnome.

The Barenaked Ladies made a children's song with that exact premise.

G for Gnu

TIL English doesn't pronounce the G in gnu. Wild language.