Use the powertop tool. Make or find udev rules to make those changes permanent. Be careful with USB auto suspend, some devices fail to resume. Once you have PCIe and SATA set to low power then Intel integrated GPUs with a Linux kernel 4.8+ can automatically go into PSR and that saves a lot of power.
And this is why I look forward to a future where most laptops have USB-C: because then you can just hook it up to any decently-sized external battery pack, and extend your runtime with an hour or two. Per pack.