Well, we gave each girl a candle to light--this was done in the leader's garage, we discussed fire safety, the girls were REALLY careful because it was a huge deal. However, this was with Junior scouts, not Brownies. YOu might want to give each girl a carnation--inexpensive yet special.
When we did Try-its, we always did them as a troop, unless, say, someone earned one at camp or something. We discouraged working on their own, mostly to keep it from becoming a competition. You may not believe that it woudl, and among the girls, it really doesn't, but there are moms who take it VERY seriously! One of DD's clssmates got written up because she earned every Try-it--her mom was the leader, and that was her goal. We earned a lot fewer in our troop, but we did other stuff, too.
For badges, the girls can earn them on their own, but a leader other than your mom has to sign off on your work--again, to avoid competition among moms and also so nobody can accuse a girl of just letting her mom hand her badges. Again, it happens. So, when we pass out badges, the main leader will hold up ones that only one girl earned to show the troop, mostly to encourage others and some are just so pretty. Besides, we think a girl should be acknowledged if she worked hard and earned more. However, if your group is younger (we're mostly 5th graders now), you may want to gloss over the differences.