'Spooner or Later' by Paul Jennings and Ted Greenwood
'Spooner or Later' is an excellent book but I've been unable to locate anywhere that currently stocks it. I presume it has gone out of print which is a real shame. If you can get hold of the text then the activities below work well. If you can't you can probably adapt the activities.

Activities using this text

Use this text to get children to play with words and to encourage thinking about the initial sounds in words. Play swopping the initial sounds and think about words in the same "sound family".

Initial examples involve the same spelling, simply swapping initial letters.
e.g. Catch a hat -> Hatch a cat

Further examples switch the sounds and also alter the spelling.
e.g. Bird in the hand -> Herd in the band

Examples such as
Rude gnat -> Nude rat
are good for exploring silent letters.

Using the text

Large pictures involving searching for information and trying examples.

Use the pictures as clues. What does the picture show? Does this fit for what we're looking for?
Encourage trying different combinations, saying/writing possible spoonerisms.

Other Activities

Spoonerism game -> One person says a "phrase" and partner then repeats phrase but switches around initial sounds.

Pass the spoonerism -> Could be done orally. Works well written. First child given a suitable starting sentence. He/she must change the intial sounds of two of the words in the sentence (extension rule: must make 'proper' words). Then the sentence is passed on to the next child who has to try and create another spoonerism. (Rule: can't change the same two inital sounds back). Sentence is passed either back or forth or round a group. (Possible aim: How many different sentences can be made.) (Discussion points: how to spell 'made up' words - relate to known spellings)

Make up own examples of spoonerisms and draw them.