Customs & Sight Security Issues...

"Customs", as opposed to immigration control, is mostly just walking through a "Nothing to declare" stall. Plus, the EU is far less strict about importing food products for personal use than the US. Nobody will even ask. Although peanut butter isn't widely eaten in Europe, the Netherlands is an exception. Unless there's a particular brand you want, you can easily buy it a jar at an Albert Heijn grocery store. Look for "pindakaas".

My observation/experience is that nobody cares if you have a tripod of any size. Some places will prohibit its use, however. As for airline security, when my tripod goes, it goes in the carryon with the other camera stuff and it's never been questioned. Nor has the monopod. But, figure this, the collapsible hiking stick (spur tip removed) has been chunked a couple of times.

Unless the peanut butter is in a jar smaller than 3 oz. you will have to have it in your checked bag, not carryon. Same for the Ensure (except for the amount you might medically need while in flight, and you might need documentation for that). As for the tripod, it should be OK to carryon (though safer in a checked bag). I don't know about the places you mention, but many places prohibit the use of tripods.

Many tourist sites do not allow the use of a tripod, but if they allow backpacks, they will allow you to carry the tripod inside. Some museums/sites make you check backpacks.

Having just been up to the top of Notre Dame, I don't think a tripod would be at all a problem. There are some amazing views from up there. http://flic.kr/p/cutpU5 But space for much of the climb, especially when working your way across from one tower to another is pretty tight and you'd just have to make sure you're not blocking the flow. There are a couple of places with some steps you can stand on that are at least somewhat out of the way. Once on the very top of the tower, it's better. But remember, that's a good 200+ steps to the top, and the same coming down. For other good views, consider the top of the Montparnasse tower. I heard much more freaking out by guards and such about flash photography, and never heard anyone complain of tripods. As long as you're not blocking anyone, I don't see those places making a fuss. For the peanut butter, you may want to think about some of the small individual packs of peanut butter I've seen advertised. Pack the big jar, and carry on the small packs. I'm assuming this is medical in nature. Since peanut butter is not liquid or gel I don't see it being a problem, but the small packs should be fairly discrete and not cause anyone to think "should this be ok?"

Regarding peanut butter - of all the times I've flown internationally, the ONLY times my luggage has ever been subjected to a security search without my knowledge was when it contained a couple jars of peanut butter. Customs definitely didn't care. It was a security thing ... it was in my checked suitcase. My TSA locks were opened and relocked. My stuff was thoroughly gone thru, and they put a sticker on my suitcase to let me know they'd been in it. I assumed it was the metal lids to the jars that showed on the scans, but then someone told me that people try to fool drug dogs with the smell of peanut butter. Not sure if I believe that, but whatever... There weren't any other problems with it, and I will still bring peanut butter in the future ( my cousin has a favorite brand ) ... But it won't surprise me if i find another sitcker on my bag @ the luggage carousel.

"...Since peanut butter is not liquid or gel I don't see it being a problem..." Don't assume anything when it comes to airport security. I had a jar of jelly confiscated at Schipol Amsterdam last March becuase it was over the 3 oz. "liquid" limit.

Tripod should be no problem as far as airline security goes. Same for Notre Dame. We have encountered two photo freak out places in Paris. The guards at the Sacre Couer go positively apoplectic if it appears you might even think about taking a photo of any sort. No photos, flash or not, no matter what. We watched one guy lower his camera, then raise it again, then get escorted directly out of the church. Versailles is very picky about their ban on tripods. My young son has a 6 inch gorilla pod he uses as a handle for his small digital camera. They spotted it when my bag went through the xray and were going to confiscate it! After much discussion, I disconnected it from the camera and convinced them it would remain in my bag, so they didn't take it away. So, absolutely NO tripods allowed at Versailles.
In general, just watch for signs as you enter the sites and follow the rules as posted. They do vary.