By "harrow drag" I'll assume you mean a spike tooth harrow (not to be confused with spring tooth harrow or disk harrow).

Since you already have a disk, you can use that to bury larger seed such as rye, oats, wheat, corn, beans, buckwheat, ect, just by adjusting the height. You can then roll over it with the cultipacker to establish good seed soil contact.

For smaller seed, (if you don't have a drill) like clovers, rape, trefoils, brassicas, ect, just broadcast on the surface and roll the cultipacker over the top to press it into the soil.

Since you already have a disk harrow, a cultipacker would be more usefull than a spring tooth or spike tooth harrow for your next peice of equiptment.