fu' - full, is used where one would say "so." So dainty, etc. Electric Scotland has this for Duff's original version:

LASSIE WI' THE YELLOW COATIE
James Duff

Chorus
Lassie wi' the yellow coatie,
Will ye wad a muirlan' Jockie?
Lassie wi' the yellow coatie,
Will ye busk an' gang wi' me?

I hae meal and milk in plenty,
I hae kale an' cakes fu' dainty,
I hae a but an' ben fu' gentie,
But I want a wife like thee.

Tho my mailen be but sma'.
An' little gowd I hae to show,
I hae a heart without a flaw,
An' I will gie it a' to thee.

Wi ma lassie an' ma doggie,
O'er the lea an' through the boggie,
Nane on earth was e'er sae vogie,
Or sae blythe as we will be.

Haste ye, lassie, to ma bosom,
While the roses are in blossom;
Time is precious, dinna lose them,
Flooers will fade, an' sae will we.

Final Chorus
Lassie wi the yellow coatie,
Ah! tak' pity on your Jockie;
Lassie wi the yellow coatie,
I'm in haste, an' sae should ye.


Lassie wi' the yellow coatie was a country dance tune, there are versions going back to David Young MS of 1734, there are versionsin Bremner's Scots Reels or Country Dances (1757) James Aird's Selection of Scotch, Irish, English and Foreign Airs v. 1 (1784), Oswald, etc. Traditional Tune Archive has these online.