Compass.

11 times. It chimes at zero and then once every second for 10 seconds.

13112221

A carrot

14 because it's twenty sick sheep not six.

None. If you put a book in it, the bag is no longer empty.

1. pour 5 litres from the 8-litre to the 5-litre bowl,
2. pour 3 litres from the 5-litre to the 3-litre bowl,
3. pour these 3 litres back to the 8-litre bowl,
4. pour the remaining 2 litres from the 5-litre to the 3-litre bowl,
5. pour 5 litres from the 8-litre to the 5-litre bowl,
6. pour the missing 1 litre from the 5-litre to the 3-litre bowl (there should be 4
litres left in the 5-litre bowl),
7. pour the 3 litres back from the 3-litre to the 8-litre bowl (and that’s it – in 8-litre
bowl 4 litres).

It wasn't raining

Onion

Fill the 5-litre bowl and overspill water to the 3-litre bowl, which you empty afterwards.
From the 5-litre bowl overspill the 2 remaining litres to the 3-litre bowl. Refill the 5- litre bowl and fill in the 3-litre bowl (with 1 litre), so there stay the 4 required litres in
the 5-litre bowl.

A shadow.

A bottle.