One thing I cannot do without is a pencil and a shorthand notebook - OK then, two.
Even if I'm working ordinary stocking stitch, I write lines of numbers from 1- 10; 2 - 20, for the rows and tick (check|)them off as I work. It helps alot of I'm knitting the fronts of cardigans and want to be certain I've knitted the same number of rows on each side, say, when I get to the decreases for under arms and necklines.
If I'm working with a pattern that has just a few rows, and is just a few repeat stitches wide, I write out each pattern row on a separate line and use a different coloured pen to mark off the pattern, like this, using a tick mark or cross
Row 1 - Pattern Stitches X X X
Row 2 - Pattern Stitches X X X
Row 3 - Pattern Stitches X X
Row 4 - Pattern Stitches X X
Looking at that, I know that I've just finished row or round 2 of the pattern and how many rows or rounds I've knitted so far (10).
Using different coloured pens means there's less chance of mis-reading how many rows I've worked; writing out the pattern helps to get it into my head and saves me having to battle with sometimes very small print.