If its broken, replace it! I have retired a pair of 1460 Doc Martens & a pair of Chuck Taylors this year. I am not big on repairing footwear as its easier for me to just go start another chapter with another quality pair of shoes/boots/sneakers. I am a fan of using the right tool for the right job, often I will have a pair of boots on my feet & a pair of Converse all stars stuffed in my pack. The sneakers are usually a godsend on your feet after many miles of walking with boots & your pack on uneasy terrain. Military boots can be resoled & in theory so can any pair of quality leather boots. I have had my insulated work boots for a dozen years & the vibran soles are starting to dryrot. Since I live in the US & we are so consumed with being consumers we have a steady supply of almost new footwear in our thrift stores or craigslist that we gotta be patient & search for. I just got a pair of worn once adidas skate shoes for $14 from a consignment boutique that I had cash credit with so I got em for free.
As far as cheap flip flops I have carried them too in the summer where I want to again give my pigs a break or if near the water where I don't want to be taking boot son & off all the time. I wont be traveling in flip flops tho. I have a few parameters to swap my footwear out. If I can smell my stinky boots when they are tied & my feet/socks are clean. (don't skimp on materials of Boots unless you are vegan/Leather footwear will last & stink less than manmade matrerials), for Sneakers its always the soles. I won't mention all of my failed attempts with shoo goo but I have been there, it don't work given the amount of weight & distance my footwear has to endure. Resoling can take time & can be expensive. I can always find what I need if I am always constantly looking for it. Life has taught me that if I know my shoes/boots are on their last leg waiting until they have crippled my mobility to address the problem is too fucking late.
More importantly is taking advantage of replacements at the right time. If you see a pair of quality north American made leather work boots in your size/style for $10 bucks that figure out how to get the money to buy them. Chances are that when your boots wear out you wont be able to find anything in your size & budget. Be proactive even if your boots/shoes aren't completely worn out yet. You can always carry both pairs or just ship 1 pair to a friend/family member to hold on to them.
Since we all use different modes of travel & battle different terrains & climates it is user specific as far as footwear choice that I think we have other threads that touch upon that subject. The reality is if you are hitchhiking/hopping freight trains you need a pair of quality work/military If you are backpacking threw Europe you may want some hiking boots. If you are on a bike tour then you will have some cycling shoes depending on your pedal choice or a skate shoe with toe straps etc.
Since there are few types of footwear that are truly versatile for traveling all of lifes climes & places on its multitudes of modality. Remember these tips. (1) right tool for the right job (2) the time to buy is when you see it (3) Replacing in advance is better than trying to repair after its too late ( be proactive)
I have some temporary solutions that work at solving a broken/lost pair of shoes in an urban/suburban situation. Bowling shoes can be rented for a few dollars, are leather & kinda stylish. They make great dancing shoes too, so next time you have a date/ swap out your unwanted sneaks/shoes for a couple dollar pair of bowling shoes. If you are in the city, simply walking around barefoot will most likely get you enough attention while spanging to get a pair of shoes/sneakers kicked down or the cash to buy a pair fairly quickly.
