Bras I don’t buy that often because having the size breasts I have and the fussiness I also partake in, causes me to not be able to find great bras THAT often. I recently left one in a hotel so HAD to go buy some more. Did not enjoy it and the bras are shit. I have been known to just reorder the same bra in each colour every 6 months.
Knickers, I buy these quite regularly. I go through a lot of pants.