What is allowed as airplane carry-ons?

For guidance, the Transportation Security Administration refers travelers to its “Can I bring it?’’ Web page, which features a search tool that addresses what items are and are not permissible on airplanes. Here’s a sampling of TSA advice. Keep in mind that even if an item is identified as generally permitted, the TSA cautions “it may be subject to additional screening or not allowed through the checkpoint if it triggers an alarm during the screening process, appears to have been tampered with, or poses other security concerns. The final decision rests with TSA on whether to allow any items on the plane.’’

FOUNTAIN PENS – Sharp nibs and all, fountain pens are designated as acceptable to carry-on, but too much fountain pen ink might not be. The ink is subject to the basic guideline: “You may carry liquids, gels, and aerosols in your carry-on bags only if they adhere to the 3-1-1 rule: containers must be 3.4 ounces or less; stored in a 1 quart/liter zip-top bag; 1 zip-top bag per person, placed in the screening bin.’’

MUSICAL INSTRUMENTS – While some airlines don’t allow separate seats for large instruments, those that do are not breaking TSA rules. Note, though, that while the listing for “cello’’ says “Check With Airline Policy,’’ the instructions for both “tuba’’ and “marching tuba’’ state “Check Only.’’ All instruments must be screened, and passengers are encouraged to be present. Airlines often recommend travelers allow an extra 30 minutes for this.

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KNIVES – If it is deemed sufficiently dull by officials, you can bring a knife to spread your butter. The other 30-odd knife species listed by the TSA will need to be packed in checked luggage. That, brides and grooms, includes the “wedding cake knife set.’’

SCREWDRIVERS, HAMMERS, OTHER TOOLS – The TSA classifies most common tools as “Check Only’’ — unless they are 7 inches or shorter from end to end

CREMATED REMAINS – The TSA promises to treat them “with respect,’’ no matter if they be human or pet remains. They are a definite “Check With Airline Policy’’ item. Not all carriers allow ashes as checked baggage. The TSA says that “under no circumstances’’ will an official open a crematory container, so travelers who have determined that their airlines will allow transport are urged to use lighter-weight material, such as wood or plastic, during transit. If the container material prevents screeners from identifying the contents, the container will not be permitted.

BABY FORMULA, BREAST MILK – Powdered or liquid baby formula and expressed breast milk are all identified as calling for “Special Instructions’’ by the TSA. Classified as “medically required liquids,’’ baby formula and breast formula and milk are allowed “in reasonable quantities for the flight’’ — beyond the usual 3.4-ounce-limit for most other liquids — and need not be in zip-top bags. (The TSA guideline: “You may carry liquids, gels, and aerosols in your carry-on bags only if they adhere to the 3-1-1 rule: containers must be 3.4 ounces or less; stored in a 1 quart/liter zip-top bag; 1 zip-top bag per person, placed in the screening bin.’’) Passengers should alert security and airline officials about the liquid at the beginning of the check-in and screening process, as many airports have special lanes for families requiring additional assistance. (Breast pumps are generally allowed in the cabin.

LIPSTICK, TWEEZERS, NAIL CLIPPERS – Many personal items that were once in danger of confiscation are more likely to be acceptable these days — just don’t try to bring on any scissors longer than 4 inches.

FISHING RODS – Generally they are permitted though passengers should check with individual air carriers to confirm that rods fit within size limitations. Sharp tackle, such as large fish hooks, should be wrapped securely and packed in checked luggage.

PARACHUTES- Be prepared to open the parachute for inspection if asked, so allow around 30 minutes for this.

CAKES AND PIES – Permitted, but “could require additional screening.’’

SNAKES – And monkeys, cats, dogs, and other live animals: “Check With Airline Policy.’’