In addition, win large drills, and something to keep them in? (7)

'something to keep them in?' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'in addition win large drills' is the wordplay.
'in addition' becomes 'too' (I've seen this in another clue).
'win' becomes 'bag' (I can't explain this - if you can you should believe this answer much more).
'large' becomes 'L' (eg in clothes sizes).
'drills' indicates putting letters inside (to drill can mean to make a hole in something).
'too'+'bag'='toobag'
'toobag' placed around 'l' is 'TOOLBAG'.

'and' is the link.

Can you help me to learn more?