7 IS-LET : If something "is let" it is occupied
9 INFO : "skinny" in this case meaning "information" - a 4-letter anagram shouldn't have been too trying
10 GAME-KEEPER - Someone brave is "game" and in soccer a 'keeper is the only one who can have the number one on their back
13 ATILLA - sounds like "A Tiller"
15 GIFT - German for poison is "gift" and you're always told to beware of Greeks bearing gifts. "Gift" in Swedish means married - but I thought that would be too obscure
17 S(TAR)S - "tar" is a sailor. A ship is an "SS" in crosswordese e.g the SS Titanic. The "stars and bars" was the old Confederate flag(standard).
18 ROSE - too easy
19 BERLIN - Irving Berlin - Bing (25) Crosby was dreaming of a "White Christmas"
20 ESS-TEE-MED - Sounds like S and T and then the Swedish for "with" (gave into the temptation to do something Swedish - so sue me)
23 DRUMMER-BOY - Bing (25) with David Bowie pollute every Christmas with this one.
26 T(I)VO - TV is the box, put 1 in to make TIV and then have 0 on to make TIVO - a digital video recorder.
27 E-PROM - a type of computer memory that keeps what is stored after the electricity (current) is switched off
28 NEOCONS - "Neo Conservatives" are the American right-wingers who made xenophobia and intolerance fashionable for a while - anagram of (no cones)
1 SUBORBITAL - anagram of (Rabbit soul)
3 OGAM - an ancient kind of rune writing. It's (No game) with the first and last letters removed.
4 SICK-BAYS - A BAY is a reddy/browny horse
5 BLUE - my attempt at a quadruple definition - probably too easy
6 DONNA - sounds like Donner
8 TREBLES - a treble definition ...
12 SLADE - reference to the start of "(So here it is) Merry Christmas" and an anagram of "leads"
14 TURKEY-TROT - A Trot is a Trotskyite or generally someone who is slightly to the left of what is comfortable for you.
17 SUNBEAM - anagram of "Ban Muse" and refers to the children's hymn "Jesus wants me for a Sunbeam", sent-up by the Vaselines and made famous by Nirvana
21 T(OYBO)X - the state is Texas (abbreviation TX), the rest is an anagram of "Yobo"
22 ELVES - steEL VESt.
24 MARX - start with "Mary" (the original Madonna) and change y to x (change the variable)
25 BI-N-G - Someone who is "Bi" swings both ways, and NG is No Good in crosswordese. Reference to Bing Crosby, who I am accusing of nothing of the sort.