I would just like to add that if you do not buy a infant carseat you will be saving at least $80 so i think it would be worth it to put that money towards the decathalon which your dc will be using for at least 5 years, unless they are very big. If you go into a restaurant i would put my ds into his stroller, and even the people that i saw who brought their infant carrier into the restaurant i saw it in the stroller, not on a chair or anything. I also have heard of this chair called the bumbo chair that your dc can use once they are able to hold their head up themselves that you could get and bring to put your dc in. Also when you bring a baby into a restaurant unless they just fell asleep or something it is quite likely that you and your dh will alternate eating and holding the baby. This is what i did with my dh.
hth
btw i agree with what paris told u to do :-)