I like Oscar rivets, a type of blind rivet with a split shaft that widens out behind 1/8" luan plywood when installed. They're made for use in RVs and are available from online RV parts vendors and Amazon. Not exactly cheap but they are very strong and great for things that are heavy or need to be well secured in place.
Ordinary wood screws work in some cases but it depends on what you are trying to mount/install. RV manufacturers love to use #8 cabinet makers screws everywhere as a "one size fits all" fastener. I have an assortment of different lengths and sizes of small wood screws that I've used on various projects which are kept in the spare stuff drawer in our TT.
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