One for ATC, second set on the ground for the OPS frequency, in the air to 121.5, third is fixed on ACARS. ATIS? ACARS if possible, if not one pilot switches on the second set to the ATIS frequency and copies the information, except if you fly for ryanair that is, just ask on the main ATC frequency blocking it for quite some time. METARs are always available via ACARS, same as TAFs.
Fuel and handling is ordered via ACARS, however, even then you can switch on the second set to the company frequency and afterwards back to 121.5.