Is there any way to import a large amount of items into a pick list?
You can use the data import wizard to add values to any table, including tables uses in picklists.
You would need to check the picklist to see what object it is using, then import into that item.
A picklist is really a 'Select <display field> from <business object>' statement
1. Identify the object the picklist is configured to use.
Once identified, you can select that object in the data import.
You may have to also examine the base object you are inserting to verify any required fields needed to insert the record as these would need to be added to the import file.