Happily Vogue's 1960s suggestions for a hospitable guest bathroom are still relatively attainable. The basic idea is to supply your guests with "everything they may need or want, within reason," so that they don't have to ask for any necessities or conveniences.
The most crucial elements are sufficient towels and a bathmat. "Terry cloth robes (hung on the bathroom door) are almost always used and appreciated, although admittedly they are a luxurious touch."
"Good soap in bath and hand sizes should be provided -- but guest sizes are a miser's invention." Ideally the soap should be brand new; worn-down slivers should be avoided at all costs.
"An efficient nail brush is indispensable, and so are a supply of fresh toothbrushes and a tube of toothpaste."
"A guest bathroom should have at least one electric outlet, and it is thoughtful to provide a magnifying mirror and a shower cap."
Two or more drinking glasses and tissues are vital. An extra roll of toilet tissue should be stored in an obvious place.
"The medicine cabinet can be as well stocked as a drugstore" if you choose and if your budget allows. "These items are basic: aspirin, iodine, a stomach settler, small adhesive bandages, and dental floss." Also consider "sun oil and sunburn soother." Cotton balls, bath oils and bath powder are other nice touches.
"If a guest must share a bathroom with one or more family members, he should be given a towel bar, even if this means that family towels must be removed and temporarily kept in bedrooms."
Any family bathrobes or nightclothes should be removed too. "All personal litter such as razors and combs should be neatly stowed away," and guests should be offered space to store their toilet kits. "Many a guest has gone without a drinking glass or tissues rather than bother his hostess or call attention to an omission that might possibly embarrass her."
All quotes are from Vogue's Book of Etiquette, 1969. This is the first passage I've come across where cigarettes were nor referenced. But note the mention of sun oil rather than sun screen.
Image one above is a bathroom designed by Schuyler Samperton
Image two, Carolina Irving's bathroom as seen in World of Interiors
Image three, a Tim Clarke shower as seen in House Beautiful 2003
Millicent Fenwick's version of Vogue's Book of Etiquette, 1948, is available through Amazon, and several readers have found the 1969 edition at rock bottom prices through eBay and other online sources.