How do I print multiple items(sales/purchases invoice, estimates, contracts, cheques, direct deposit stubs...) at one time?

Select Setup, Settings, Company, Forms.
Under the column Print in batches, put a checkmark on the transactions you want to be able to print in batches.
Select OK. There will now be a new report option in the Reports menu.
Select Reports, Print Batches.
Refine display options and click the Display button to view a list of items that match the options selected.
Select all the items to be printed by putting a checkmark beside the transaction number or using the Select All button.
Select the Print button.