I'm taking a trip to Paris in the summer, the trip will last a total of 2 months. The flight I plan to take is from Charlotte to Boston, then Boston to Reykjavik, then Reykjavik to Paris.

Will I have to go through customs on the way to Paris at any time? And when will I have to do it on the way back. I read that it's only necessary when entering the US, but I don't know if that's entirely true. I plan to buy some basic things while in Paris, clothing, cosmetics, and footwear. I know about the $800 exemption, I think it is, and I'm just worried that I will go over that. What would the charge rates be on items such as those and what are the methods of payment that are available to me and where would I have to do that? (yeah, a little pessimistic and anxious of me, but, I'll be honest, it's my first flight on my own, much less international flight on my own)

I'm confused as to if customs asks for declaration in Reykjavik and they do it again in Boston, would the exemption be counted as already used since/if it happened at a connecting terminal?

On a second note, the layover in Boston is 8 hours, what am I allowed to do during the time? Am I supposed to just carry my carry-on around with me? Can I leave the terminal and return when my flight is ready? Are there any security proceedings that I might encounter, not just during the layover, but overall, to and from?

Thank you very much, and I'm sorry about the anxiety, I'm just a little/lot nervous.

On the way to Europe, you will go through passport control (immigration) in Reykjavik and then customs (possible luggage inspection) in Paris. Iceland and France both belong to what is called the Schengen Area, a union of 25 European countries that have effectively eliminated borders between them as far as travel goes. Since Iceland is your first port of entry, that's where you will show your passport. I'm sure you'll go through airport security in Reykjavik too. If you check your luggage through, you won't see it until you get to Paris.

On your return, you'll go through passport control in Boston, since that's your first port of entry to the United States. You'll retreive your checked luggage and go through customs there too. You'll then be outside airport security and have to go back through security to get to the gate for your final flight back to Charlotte.

www.travel.state.gov France for best precise info on Paris

Headed there in April go a lot...

You will pay any duty overage as you enter when you get back

Not bad just be honest so no worries...

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They get VERY nervous/picky about that.

You may find this leaflet from French Customs helpful:
http://www.douane.gouv.fr/data/file/5461.pdf

You will go through Customs in Paris - which in reality means that you pick up your luggage at baggage claims and just walk out through color-coded exits - either the green one for "nothing to declare" or the red one for "goods to declare".

If there is a third exit for arrivals from the European Union (usually in blue and/or with the EU flag) you may not use that one unless it is (as often) a combined exit with the green sign for "nothing to declare". It sounds much more complicated than it is.

You can check the leaflet for the allowances, but aside from duty free goods which are limited in quantity, you can bring all your personal belongings into France without paying duties.
Only when you, for example, bring (expensive) presents for your hosts in France (or any item that is supposed to stay in France), you may have to declare those if the value exceeds the limits.

Alright, so customs in Paris on the way there, and I don't plan to buy anything during any layover so I should use the "Nothing to Declare" line? Is that right? Does that basically mean that I get my luggage(s) then proceed through customs before leaving the airport?

Passport control in Reykjavik shouldn't be a problem, right? What does that usually entail, in terms of what I might need? And would I have to do the declaring thing in Reykjavik as well as in Boston?

Also, when buying cigarettes in France, would a U.S. issued ID suffice, or would I have to use my passport as means of identification?

Again, I apologize for the obviousness of my first-flight-alone anxiety.

Passport control in Reykjavik will be just that: You show your passport. You may or may not get it stamped. (Probably will.) You will then go through security (x-ray, metal detector, all that) and will go to your connecting flight to Paris. They won't be concerned with the goods you're bringing in at that point because you are not entering Iceland. That won't happen until you get to Paris. You'll claim your bags and go through customs there. As was pointed out, you shouldn't have anything to declare. You won't show your passport in Paris because you've already taken care of that step in Iceland. Remember: It's essentially "border free" travel among those 25 countries, and includes France and Iceland.