Bottle of Water = Attitude Indicator
If the pilots did believed "all indicators are down" then they could have used a bottle of water to get a rough idea of horizon. It would give an instant sanity check on the pitch and bank.
If you think you are -45 deg but you look at the water level shows +45 then you are likely to change from pull stick try to push stick. When you do so and the water level instantly responds gradually returning to level. The pilot then has a feel for the spacial orientation of the a/c in the absence of a visual horizon out of the window.
The jostling of the airframe would move the water around however I believe it would be enough to approximate in the absence of any other indicators.
It really sounds like they had no instrumentation or at least did not trust the stall warnings. Otherwise they would follow the stalled checklist.
GPS gives the ground speed and direction. Again not ideal but better than nothing. Clearly the pilots were way out of the normal trained situation and flight envelope.
A few comments refer to "seat of the pants" flying. This has itself caused incidents when pilots don't look at the instruments and instead rely on gut feel. The mind plays nasty tricks when you experience acceleration without visual reference points.