For some of the clues you need to know that  
1 is A, 2 is B…….. 26 is Z   your
The anagrams are mostly connected with Christmas   course
 and it is the missing letter you want.  
  letter number
1 G G Deadly sins   at on
2   D 500   control map
3   E What is 42 - 37?  
4   K 1024        or       2.2 lbs    
5   H Snow White and the Dwarves   start
6   C A R R E K C *   A  
7   I ___s and ears and chin and mouth and nose   B  
8   B May all your Christmases __ white   C  
9   X S M A *   D  
10   W C O R G I   A L L E Y   *   E  
11   M _ _   F  
12   S . . .   G 1
13   U  2 x 7 x 6 / 4   H  
14   T ...and everything stops for   __   I  
15   V According to Caesar, C/XX   J  
16   L Fifty   K  
17   R Wherefore art thou __   L  
18   Q Person,person,person,person,person,person   M  
19   N S A T  C A S U A L    N  
20   O G I S T N K C *     O  
21   Y E squared   P  
22   Z Type of bed   Q  
23   A Alphabet minus bravo-echo-tango   R  
24   P Lathyrus (bot)   S  
25   J Romeo & __   T  
26   F A dance originated in 1914   U  
  V  
  W  
  X  
  Y  
  Z  
  finish