We being long (very long!) past child bearing age I now use the infants
bottles for measuring oil for our 2 cycle chainsaw.
One side is graduated in millilitres; very useful since we buy our fuel in
litres! But no trouble at all to mentally caculate a 40 or 50 to one oil/gas
ratio etc. for US or Imperial gallons!
The feeding bottles have the advantage that on many, an ordinary, old
fashoned, baby food jar top will fit.
So an extra 'charge' of mixing oil can be carried compactly and safely; in
a haversack if necessary!
Some of the old bottles were/are glass but some were plastic and less likely