Presumably to remind us that they were there at one time in the past.
Written accounts, specifically Pliny the Younger
They left nothing behind in writing. The difference between 'prehistoric' and later peoples is that we call them 'prehistoric ' if no written information has been left to us by them or about them.
The Romans abandoned Egypt when it was invaded by the Arabs in 639-42.
Rich Romans wore a toga to outdoor events. They also had other stuff to wear.
Prasutagus did not actually leave his possessions to the Romans. He had incurred heavy debts with the Romans to finance his lavish lifestyle. When he died the creditors called in the debts.
Their organs.
nothing
yes
No that is what we call a snail.
Roads and aqueducts were abandoned in France and remained in use for years after the Romans left.
Written accounts, specifically Pliny the Younger
Go to their houses. Secretly jack the desired "stuff" behind their back. Leave the house. Go to Alaska.
The Romans left roads because they wanted the roads so that they can get to other places of Britain easier and quicker.
Toilets or latrines were part of the infrastructure of the houses and public buildings. There was no way they could be removed.
Because sometimes thay leave stuff behind from the past
they buy stuff
If it looks like a bundle of small long pods, it's fly eggs. Try and cover your food and not leave it unattended.