The most common and most likely answer to this crossword clue is the 7 plus 1 plus 5 letter word PROPOSE A TOAST
I've seen this crossword clue in The Daily Telegraph
P
R
O
P
O
S
E
A
T
O
A
S
T
More clues leading to the result PROPOSE A TOAST
Buddy explains!
The straight part
We know that "What one may do at a reception" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what one may do at a reception = propose a toast.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.