Large bars are ideal for SMSF.
For SHTF, it all depends. Early days, it's all about food, water, medicine, weapons and mobility. Mid-term, it'll be about seeds/crops, books, water, medicine, weapons and walls. Tobacco and tampons will be valued trade goods.
Once traders establish market hubs, silver/gold would likely take the role of currency where straight barter is not viable. When the store owners accept it, and dispense it, it will gain universal trade value. Until then, it is just another good to barter with. An ounce might buy a loaf from one person & not be accepted at another.
The bigger the trader, the more likely they will value gold/silver once it all settles down. Ideally they will have sufficient variation in size to give you change for your kilo, otherwise it'll be store credit.
If you are travelling long distance, and you have to bring your stash, gold will slow you down less, and is more able to be hidden within your digestive system.
PMs in a SHTF scenario would be better off stashed than bartered initially. People might not want to trade bread for it, but they will kill you for it. Leave the bulk of it stashed until things return to normal.
During the early days post-SHTF, you'd do best will small tradable items that are taken for granted now, but will be considered luxuries in times of crisis.
