I don't take the rubber cap off. The needle goes through it. I have not seen any leakage.

You don't need to do anything to re-seal it -- it has a rubber closure that will keep the liquid from coming out. It allow needles through, but it won't pour out or anything. Just put it in a Ziploc.

I just started my delestrogen injections for an upcoming FET, and wasn't sure the best way to store the vial since you keep re-using the same one. The cap doesn't fit back on to seal it, so I just used tape to secure it on, but wondered if anyone has a better way.

Also, I have to travel by plan next week, and wasn't sure if I should take this open vial or just buy a new one to use while traveling? Any advice is appreciated.