For some of the clues you need to know that  
1 is A, 2 is B…….. 26 is Z   The
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 23
7   I ___s and ears and chin and mouth and nose   B 8
8   B May all your Christmases __ white   C 6
9   X S M A *   D 2
10   W C O R G I   A L L E Y   *   E 3
11   M _ _   F 26
12   S . . .   G 1
13   U  2 x 7 x 6 / 4   H 5
14   T ...and everything stops for   __   I 7
15   V According to Caesar, C/XX   J 25
16   L Fifty   K 4
17   R Wherefore art thou __   L 16
18   Q Person,person,person,person,person,person   M 11
19   N S A T  C A S U A L    N 19
20   O G I S T N K C *     O 20
21   Y E squared   P 24
22   Z Type of bed   Q 18
23   A Alphabet minus bravo-echo-tango   R 17
24   P Lathyrus (bot)   S 12
25   J Romeo & __   T 14
26   F A dance originated in 1914   U 13
  V 15
  W 10
  X 9
  Y 21
  Z 22
  finish