To limit or restrict activity and expense items, and employees on a project, you can use the project assignments feature. To so do:

1. Open the Projects > General > Assignment screen from the side menu.
2. Select an option from the Show drop-down and click the relevant add option.
3. Select the items on the grid and click Add. All the selected items get assigned to that project. The same applies to the employees.

Now only these assigned items will appear in the drop-down lists of the time and expense entry screens for this project. Check CORE Help Center for details.