You could set up a trust fund for him and pay a bit each year into it. Other relatives and friends of the parents could pay in too. It could be paid into till he's 18, 21 or even 30. Then his college/university fees could be contributed to, or he could use it towards a car when he's old enough.
Like Sir Alec says, any kind of investment would be a really valuable and practical gift. But as an additional, more personal item, what about a time capsule based on his birth date or christening date - newspaper headlines, fashion cuttings, music, lifestyle tips - to be opened when he's 18. That will certainly give him a laugh when he's an adult
Theres always lots of christening gifts to choose from if you go in any good jewellers. they have silver picture frames for example so the parents can put the babys christening picture in it, or christening scrolls that they can get engraved,, all sorts.
kiki-frogs idea is brilliant. You could even buy several newspapers of the day to give him a different take on stories of the day as reported by papers of different politics. Take photos of all his family as they are now, including yourself (!) You'll all be amazed when it's opened in however many years you choose to lock it away for. A couple of small, current popular toys could be included. They'd be in pristine condition and maybe worth something? If you could afford one or two of the latest Star Wars figures for the new film, the original figures, if still in their plastic containers, are now worth a fortune to their mental fans!
For future presents which don't cost much, Google Hawkins Bazaar. You could make up a lovely little Christmas stocking with several of their £1 items. I wish we'd had this company when I was a kid!
I've just given my goddaughter's brother for his new baby son (last week) a mini-rugby ball, as my father gave the brother his very first ball when he was two. He went onto play for the Christchurch Crusaders and was hoping to play for Harlequins or Northampton but took a very bad thigh injury - he still plays Nat Div 3 and has become an accountant with one of the major groups.
The poor bairn was having his tongue operated on today, as he can't latch on to mum properly causing all sorts of pain for her, a wee snip of the web I would think....
So it's not the financials, fruitsalad, it's the thought and relevance of the gift that accounts, though I do think the investment idea is a good one. On a similar vein, if the parents are into wine, a share in the Wine Society perhaps, (some 50 quid) - and, later on, a bottle of port or two if 10`5 is a declared vintage - or good Bordeaux.