SOPs are packs off. Switched off during line-up, turned on again after setting of climb thrust.
If we decide we need the packs for whatever reason, its packs on engine bleed, nothing else.
Engine bleed off or APU bleed on might work fine as long as you don't encounter icing conditions. APU bleed is not authorized for wing anti-icing, as it simply does not supply the required temperature. Engine bleed off is self-explanatory. This might pose a risk in a high workload / stress situation.