Leveling Parts of the Yard

Mason sand and a lawn leveling rake.

How little is little?

If really just some small areas you need to smooth out, then Mason sand and a leveling rake is probably the best. You can buy small bags from HD/lowes etc. If you deep holes to fill then you can get some top soil, preferably from a landscape place. Most bagged top soil is just composted wood products and will continue to breakdown, making the level process not worth while. So would try to avoid bag products if possible unless it's just such a small area.

If you have a large area to level or want to level the whole yard. Then you can get deliveries of Mason sand from either landscape places or even gravel places. General rule is 1ton per 1000sq ft.
If you get it from a landscape place, you can probably get it mixed as well if you want to change the texture a bit. Something like 70/30 sand/topsoil(or compost) is probably what I would do.

Other thoughts is that you can get bags of sand delivered from places like lowes(they do 1/2 ton bags). Or you can do places like soil3 which will also deliver a level mix. However you pay a premium for this, but it is convenient to have it in a large bag which you can work on over time instead of it being dumped on your driveway.