Not eating chametz that was sold to a גוי
This has become a very popular chumra in Israel in the past few years. In fact, for the past few years the major bakeries accomodated this chumra. Flour used in baking is washed before used which makes it into chametz. Therefore, the major bakeries (Angel's, Berman's, etc.) would use only unwashed flour right after Pesach until they received flour that was ground after Pesach. This year both Angel's and Berman's decided not to do this, they felt that it was too much work (the flour was hard to use and didn't bake well) and therefore after Pesach they used regular flour. This caused an uproar in certain segments of the Charedi community, there was a big article about this in the Mishpacha magazine this past week how it is terrible that this year we went backwards in terms of chumras.
Interestingly enough, the Badatz Eidah Chareidis (who gives the hashgocho on the bakeries) has no problem with this. They hold that the sale of the chametz to a גוי(which they arranged) is perfectly valid and therefore there is no reason to be machmir.
This is one thing that we can all learn from the Eidah Chareidis. they have their shitos and they hold from them. They don't care if other people are machmir, if their poskim hold it is mutar, it is mutar and they offer no apologies. The same thing applies in shemittah. They pasken that non-Jewish produce has no kedushas sheviis, while many in the Yeshivish community are machmir like the Chazon Ish that the produce has kedushas sheviis. Again, they follow their mesora with no apologies.
The serious MO community needs to take a lesson from them and follow their rabbanim בין לקולא בין לחומרא and not be influenced by the chumra of the day attitude in some parts of the Charedi community. If the MO poskim like RHS, RMW, etc. are matir then don't apologize, follow the poskim with pride.