To guarentee you will have enough for your, or anyones needs, I've never heard anyone complain there was too much seed in the packet, but they may complain if there wasn't enough to recover for first sowing failure. You can always save some for next year and the year after. Some seed packets don't contain much seed, the little gem squash I grow only has eight seeds in the packet, although that is more than enough if we have a summer like last year.
I'm glad that packets like carrots have a lot of seed. I probably sow well over 1000 carrot seeds each year, and get about 20 carrots.
What you could do is ask around if anyone would be interested in starting a seed swap. We have one in Horsham every year where people can drop unwanted seeds in exchange for a packet of something they do want.