Special keepsake gifts

I have recently read an article about how coin collecting is becoming fashionable again. How about a commemorative gold coin? Or a gold nugget? It would become more valuable in time, just like the girls´ bracelets.

Thank you all for your responses, apart from scoutingand saxophone playing he has no special hobbies. He does love films and I considered an original poster or signature but worried about authenticity.

I know watches have been made almost obselete as everyone looks at their phone to find the time, but my sons still wear their "good" watches that they acquired for their 21sts or 18ths etc when they dress up for weddings etc.

He may not be into adornment at the moment but something like a plain men's bracelet /bangle/cuff would be a keepsake and he might 'grow into' the fashion. You could have it engraved.
I know older teen boys who wear this type of thing
www.alfredco.com/shop/mens-jewellery/mens-sterling-silver-torque-bangle/?gclid=CNeA1Lvu4NQCFc-77QodfeALhg

Does he have a hobby? Something maybe to go with that. A really good leather wallet. If he reads a first edition book or limited art print/poster .

This is always a difficult one, as many young men nowadays don´t wear watches or cufflings or gold chains, which used to be the traditional keepsake gifts for boys. I was surprised when my son (admittedly not 13 but in his late twenties), after my mother died was asked if he´d like anything from her house. He chose a brass Welsh miner´s lamp that my parents had bought as an antique many years ago and some small pictures they had on their wall. He now displays these in his flat, presumably to remind him of his grandparents. I honestly didn´t think he was that sentimental but am quite touched. How about a small painting, perhaps of a landscape or place that has a special meaning for both you and him?

Hi glass if he is outdoorsy -
what about one of those Leatherman multi-tools? You can have them engraved. (And of course it depends on whether it's okay to give him something that includes a pen knife).

www.amazon.co.uk/Leatherman-LT650-N-Nylon-Pouch/dp/B000PILWFY/ref=sr_1_12?s=camping-hiking&ie=UTF8&qid=1498631517&sr=1-12&tag=gransnetforum-21