keep an eye on the parcel
If someone say they will send a parcel to me, can I reply:

1) I will keep an eye on the parcel.
2) I will wait for the parcel.

Thank you.

Question

keep an eye on the parcel
If someone say they will send a parcel to me, can I reply:

1) I will keep an eye on the parcel.
2) I will wait for the parcel.

Thank you.

Answer

2 is better.
'Keep an eye on'  means 'look after'.  'I will keep an eye on your house while you are away'. You can only 'keep an eye on' something that is there.
Did you mean to say  'keep an eye out for the parcel'? That means that you will look for it, e.g. checking the place where it is likely to be delivered.