If you sit close to a perfumed person, ask the stewardess for another seat. You can also move yourself to a vacant seat, as soon as the plane has taken off. You can do that without asking.
You can also try to bring along a small mask, even the small "dust masks" may help a little.
You can call the airline in advance, and ask them to put in your travel information that your are 'aroma sensitive,' i.e. have problems with smells. I think they call this process documenting, which they use for all sorts of disabilities and special needs. The advantage of doing this is first that the cabin personnel know in advance that there is a potential problem, and also lets the airlines know that this problem exist - imagine one day there could be fragrance-free flights! (or at least the travel information people get could ask passengers to lets off the fragrances).
You can try to request the oldest vehicle they have on site. Rental cars gets a lot of use, so they gas off faster than cars that sit closed up all day, so a one-year-old car may be good enough.
Ask for a car with cloth seats, as plastic seats gas off more.
To get older cars, try Rent-a-wreck, they have affiliated outlets in most cities. Their web-site can help you locating an affiliate. I have used them, and been highly satisfied, and saved money too. The affiliates are locally operated, are seldom located at an airport and may not be open evenings and weekends, so there is some amount of inconvenience, and you don't really save much.
More expensive hotels, do NOT mean better indoor climate. I've stayed at a Hyatt that had NO fresh air intake in the room, the register on the wall simply recycled the room air, while sending it through a dust filter and heating/cooling the air. The front desk folks were not aware of this. When I complained about the air quality, they offered to send up a technician to increase the air flow, fortunately the technician was understanding, and opened the window that otherwise could not be opened.
About a hundred hotels/motels around the country have evergreen rooms, that are smoke free and comes with an air cleaner. See below for a listing.
Always call the hotel ahead of time, some hotels will leave the room unoccupied for you the night before (unless they are full), so it has not been cleaned right before you arrive, and lingering smoke and fragrances is gone. Ask how long ago it is since they remodeled or put in new carpet.
When you call, insist on a room with operable windows, get a firm promise that the windows can be opened, or that they will open them for you. Many times the windows can only be opened with a special key. Another way around this is to get a room with a balcony, or French doors. Also, ask about how old the carpets are, and request a room with an old carpet. Tell them the reason, they may be reluctant to put you in a room with an old stained carpet.
Here are some ideas for when you get to the hotel:
Plan ahead for other places to stay, in case the hotel cannot accommodate your needs.
Choose your site with caution, here are some suggestions:
If you don't want to say anything about these problems to the attendant, ask for a quiet corner, that is usually the best place anyway.
You may also want to ask about whether they have recently sprayed with pesticides. I have once seen a campground that actually posted the last date they sprayed.
There are books on the market listing free campgrounds. These are often rustic campsites maintained by the Forest Service, the sites are usually widely dispersed, and thus an excellent choice.
One word of caution on the use of toxic chemicals in the toilet: These may be a problem for you to handle. We used enzymes, which worked very well. Only inconvenience was the need to put a spoonful of the powder into the toilet once a day. I forgot the name of the product, we had to buy it directly from the company. We just had to ask the rental agency to fill up the sewage tank with water, so we could flush out the chemicals used by the previous renter, as they kill the enzymes.