A commonly neglected option with airline miles and other points is upgrade awards. In the below example with United, one of the options I checked had a value of 39.5 cents per point, which is relatively unheard of with United Miles, that The Points Guy values at 1.45 cents per point.
Image courtesy United
Image courtesy Google Flights
Keep in mind that the below are assuming that all flight upgrades clear, while the full refund upgrades possible aren't being considered since it's often hundreds of dollars in value at no cost when that happens. Also, the $ copays can vary considerably on the same itinerary, with higher $ rate economy fares generally incurring lower $ copays vs lower cost economy itineraries on the same itinerary. Unless you have United elite status, you won't be able to upgrade others who aren't flying on your itinerary.
Examples With United:
United Free Domestic Upgrade Policy for Non-Elites on Domestic Connecting Flights When Attempting a Multi-Leg International Polaris Business Upgrade & the International Segment Isn't Upgraded
United Examples Intro
35k Miles at 39.5 Cents Per Point in Value +$386 Upgrading Economy to Business Class East Coast US to South Africa (Waitlist)
20k Miles at 29 Cents Per Point in Value +$581 Upgrading Economy to Business Class East Coast US to Europe (Waitlist)
20k Miles at 19 Cents Per Point in Value +$488 Upgrading Economy to Business Class 2/3 Segments East Coast US to Istanbul (Waitlist)
30k Miles at 15.6 Cents Per Point in Value +$586 Upgrading Economy to Business Class East Coast US to Singapore (Waitlist)
35k Miles at 11.5 Cents Per Point in Value +$536 Upgrading Economy to Business Class East Coast US to India (Waitlist)
17.5k Miles Negative Value Example on Domestic Travel (Confirmed)
Many of the above are courtesy Google Maps or United