Solid state electronics can withstand huge accelerations - they can be shot out of a cannon and still function. So you don't have to worry about most of the components.
If you're shipping this or taking it as checked baggage on the plane, I would remove the heatsink and pack it separately (along with some extra thermal paste). It's a heavy object held onto the motherboard by relatively weak connections. If a baggage handler drops your suitcase, it could rip the heatsink right out of the motherboard. If that doesn't damage the computer, the loose heatsink bouncing around inside for the rest of the trip surely will.
The video card maybe. It's held along two edges so it should be pretty stable. But if there's a lot of weight at the opposite corner, that could create a lot of torque. A couple rubber bands fastening this opposite corner to the case would probably be good enough.
If you've got a HDD in there, I would remove it and pack it in bubble wrap. I've had a half dozen HDDs die on me over 25 years. All but one had been transported while mounted in the case, without some sort of cushioning. Just look at the oversized cushioned packaging in the retail boxes the HDD manufacturers ship the drives in. You have to figure they know something about HDDs being damaged during shipping.
Research what the lost bag compensation limit is for international flights to/from your country (how much the airline has to pay you if they lose your bag). In most cases it's laughably low (they assume your suitcase is full of old clothes). Depending on your finances, you may wish to buy additional insurance in case your computer's bag is lost. Check your credit cards to see if they automatically provide travel insurance - several do if you buy the plane tickets using the card.
If your home country has strict import tariffs, you may want to register the computer with customs before you take it out of the country. That way when you return, they won't try to claim you bought the computer on your trip, and are trying to import it without paying duties and taxes. (I would try to avoid this in the destination country by sneaking the computer past customs. A friend of mine was forced to register all his camera gear when he visited Korea. His camera bag was stolen while he was sightseeing. When he tried to leave the country, Korean Customs assumed he'd sold his camera gear and made him pay import taxes and duties on his stolen gear. There's basically no upside to you for registering equipment you're bringing into another country - most countries don't care if you take stuff out, only what stuff you're bringing in.)