One variant of the numberplate game involves spotting cars with each number from 1 to 999 in order. The letters around the numbers are ignored. In the UK, where a basic game can last many months, this will become harder now that the numbering scheme has changed.
A much quicker game is to seek the 26 letters of the alphabet, again in order. For those with difficulty finding I, Q, Z or other 'tricky' letters allowing a single numberplate with the two letters adjacent to the required letter can be allowed (thus X123HXJ can be an I as there is an H and a J on the one plate) (use Y+A for Z and Z+B for A). To make it even easier, allow triple characters to represent anything (thus with X123PPP or ABC222X the triple is a 'wild card').
To make this a competitive game between two teams, have one team work forwards through the alphabet and the other team work backwards.
A North American version of the game involves attempting to find a license plate from each state and province.