Hmmm depends on the type of game. If its more music driven like old games, you don't want too many sound effects to get in the way. When I was making my 2d project I felt the sounds weren't representing the world and the music wasn't enough, so I added some low subtle foot steps sounds and it felt so much better. I don't know much about effect packs but I am a sound designer and do enjoy designing sounds myself. (Even looking for projects too ?)
maybe tweaking sound effects to make unique to your game could work. I dont know about copyright stuff thol. As a music producer, I have played a lot with percussive samples of drums, and there are a lot of ways to make sounds that sound good in games. I've made some cool explosive and banging sounds when I was just trying to find music!