Is it possible to build laptop power adapters that are considerably smaller and lighter?
Google is running a design competition to build an inverter with a power density of 50 W per cubic inch.

It will be a while before your laptop PSU fits into an Altoids tin though. The density for the competition is still a way-out goal, nothing can do that yet. It's also a many-kW inverter, so economies of scale will dilute things like the connectors, PCBs etc.

Finally, a 90% efficient PSU still has to dissipate 10 Watts. If it got much smaller, it would have to get much more efficient too, otherwise it would get unreasonably hot (or need a fan).

Edit The winners of the Google Little Box Challenge managed \${1423 W/in^3}\$, a 2 kW solar inverter fitting into only 14 cubic inches. Not much bigger than your current laptop power supply, eh?