Short-sleeved shirts that aren’t tee-shirts. I’m in New Jersey, where for most of the year I’m in turtlenecks and often a sweater or two over that. And for exercise or anything involving grunge or sweat, there’s the tee-shirts, preferably one of the less-cool ones. But dressier or nicer short-sleeved shirts requiring ironing? Only a handful of those…
Pants. I have 4-5 dress pants so I usually end up wearing one each day. I keep saying that I’m going to buy more - but then when I do, I tend to buy ones that are more noticeable - like stripes or designed hems or something - then I feel like I can’t wear them as often without someone noticing.
If I run out of undies, I just go commando for a day or two. What??
I’m surprised that socks is not the #1 answer. I have enough dress socks to last me for about a month. I have enough MATCHED dress socks to last me about 5 minutes. I’d do another “purge and buy”, but within 2 weeks I’ll be right back to where I am now.
I have a huge amount of socks and underwear, and I don’t wash pants that frequently. So, since my armpits sweat quite a bit, that leaves shirts to run out first.
At that point, do you go bra-less? 
Socks. I do an immense amount of laundry - the machine is going pretty much every day (there are three of us and it’s a small machine) and the washing basket is never full. Yet we still run out of socks. Something seems to happen to them in between being worn and being washed.
Often I end up handwashing them in the morning and drying them gradually in the microwave.
I do the washing on alternate days, so I never run out of anything.
Pants. Or rather, pants that are appropriate for work. I have plenty of jeans, but I can’t wear those. I have quite a few pairs of dress pants, but not enough for two weeks of work.
Pants, but then I re-use them until I do laundry. Wouldn’t be comfortable doing that with shirts.
That’s generally my position, when I am contemplating using pants I’d descarded for wash, that’s when I need to set aside time for laundry.
I have less pants then any other article of clothing so I’m never in danger of needing to reuse anything else.