If you've never played the 'What If?' game before, this is how it goes. You take a common item, say an empty bottle, and you ask yourself: What if it was bigger? What if it was smaller? What if it was packed with sand from Brighton Beach? What if it was painted red with white stripes?

It's a strange pastime, this What If? game, but from it has emerged some of the most profitable products of all time, the most prominent being Coca-cola which allegedly started life as a cough syrup, rather thick, very gooey, and leaving a strong after-taste. Until someone said 'What if we add water and drink it'. The rest, they say, is history.

Here are a few What If? questions, and products they must surely have spawned:

* What if we fill it with something silly?

Tins filled with holes from Polo mints, offered as competition prizes in the 1970s, are valuable collectors' items today and like one I saw in a recent sale of advertising memorabilia they can fetch hundreds of pounds a time.

Tins filled with London Smog - a kind of dirty fog that hung across London and caused hundreds of deaths daily in the early 1950s - were offered as souvenirs to American tourists who sometimes sell them on eBay.

Bottles filled with Irish Turf sold like hot cakes to Irish-American families when they first appeared in the 1980s, before copycats moved in and killed the market.

* What if we broke it and sold the pieces?

Witness the former wooden Brooklyn Bridge, torn down and replaced by the current metal and concrete variety, which was sold piece by piece by Paul Hartunian and generated millions of dollars.

The same technique helps sell pieces of turf from well-known football grounds, pieces of meteorites (see www.themeteoritemarket.com - they sell lots of the stuff), even pieces of Plymouth Rock that sold on eBay last year at between $609 and $2165 apiece and none bigger than a walnut.

When the Berlin Wall fell a friend transported hundreds of fragments home, framed them, and sold them in pre-eBay times at 20 a time. Goodness knows what they'd be worth now with an international audience to target.

Demand and price can be inflated by linking items to specific events. So pieces of Plymouth Rock (from where originated America's Pilgrim Fathers) sold well during Thanksgiving Week and strips of turf flew out of the turnstiles when Wembley's historical football ground was closed for refitting!!

* What if we buy this stuff that doesn't sell and add it to something else that does always sell?

One hundred plus Penny Black postage stamps offered at an auction in Yorkshire last month attracted no bids, not from stamp dealers unused to selling anything quite so torn and tattered as these pathetic specimens. My daughter bought them instead, made them into charms, and sold them as charm bracelets under her 'Hobo' vintage jewellery banner with stamp catalogue value of 100 and 200 a time highlighted in her eBay descriptions. Those stamps costing a few pounds each, added 50 and more to bracelets normally fetching ten or twenty pounds each.

Here are some questions for you to answer and turn ordinary items that nobody wants into products that sell like hot cakes on eBay.

* What if we paint it red with white stripes? (Bearing in mind England's presence in the Football World Cup this year and a national flag of similar colours!)

* What if we look for anniversaries that might lend themselves to unique product ideas? This is one of the most profitable ways to play the What If? game so you'll be happy to know that this year:

- May 24th marks 100 years since the The London Ritz was founded by hotelier Cesar Ritz.

- Marmite was created in Staffordshire one hundred years ago. The 'Love It, Shove It' relationship we all have with Marmite might be worth exploiting. I'll be hunting through vintage magazines for cartoons and advertisements from Marmite's early years to recreate as prints, postcards, key rings, place mats, or hundreds of other popular items. Be careful not to break trade mark and copyright laws if you decide to copy early designs, they won't normally be public domain until 70 years after the artist's death. But why bother with copies, I recommend you stick with original items, they're prolific in early magazines.

- Poet Laureate John Betjeman was born 100 years ago, the same year that the British Labour Party was born. The perm is also one hundred years old, as is the first diagnosis of Alzheimer's Disease. And the Japanese are currently celebrating the centenary of The Book of Tea, written by art historian and curator Okakura Kakuzo (1862-1913) and representing the first study in English to explain the philosophical and aesthetic background of the tea ceremony. Now I wonder if that book is still in copyright or could I reproduce it, maybe bundle it with some special tea bags, or use it to sell vintage tableware, use it as the basis of a book I want to write about healing teas . OR WHAT IF?