I love the idea of repurposing these components. As for what you can use where, there are definitely some things you can put in other devices.
* Hard drive and DVD drive are pretty universal. You can definitely get an enclosure for the drive and use it for external storage., or even just with a SATA to USB cable (assuming it's a SATA type drive), but it will be less portable and more susceptible to damage without an enclosure.
* DVD drive might be a bit trickier since these sometimes use proprietary connections.But to use it as an external drive you probably only need a SATA to USB adapter.
* The WiFi card could be compatible with other devices, you may need an adapter to make it work in a desktop since they don't usually use the same kids of slots for expansion cards, but I'm sure it's plausible. We'll need to see what sort of card it is to advise more specifically.
* Fan/heatsink might be trickier since those are usually built to accommodate the housing of their original laptop. They could be used possibly, but would definitely require some modification.